Читать книгу North American Recent Soft-Shelled Turtles (Family Trionychidae) - Robert G. Webb - Страница 4
ОглавлениеThe means of some samples (Fig. 3) differ in regard to PL/HW, but the ranges of variation overlap so much that little significance can be attributed to the difference. T. ferox, and to a lesser extent T. s. emoryi and T. s. asper, have slightly larger heads than the other forms. The width of head is proportionately the smallest in T. muticus; in most individuals of it having a plastron so long as 13.0 centimeters, the width of the head is less than 16 per cent of the length of the plastron—a percentage that is distinctive.
The visibly narrower carapace (CL/CW, Fig. 4), suggesting an ovoid or [464] oblong shape, in some large individuals of T. ferox and T. s. emoryi is indicated by the large ratio in specimens that have a plastral length of 8.0 centimeters or more. Nevertheless, the degree of overlap of the ranges of variation is such that this ratio is of relatively little use taxonomically.
The greatest width of the carapace is farther posterior in T. s. emoryi than in the other forms (CL/PCW, Fig. 9). The considerable overlap of the range of variation of this ratio for emoryi with the other forms limits its usefulness as a taxonomic character.
The snout is proportionately shortest in ferox and T. s. emoryi, and longest in muticus (HW/SL, Fig. 10). The most marked difference in this ratio is between the species muticus and ferox; the ranges of variation of those species overlap to a degree that tends to negate the taxonomic usefulness of this character.
Most adults and subadults of T. ferox show clearly in dorsal view the anterolateral portions of the plastron. This condition is much less well developed in some specimens of T. s. emoryi. T. ferox is extreme in the ratio CL/PL (relatively the longest plastron or shortest carapace, Fig. 13). T. s. asper has the shortest plastron in relation to length of carapace. Calculated ratios for 12 T. ater average 1.36, a value that suggests close affinity with some subspecies of T. spinifer (pallidus, guadalupensis, emoryi). Because of the degree of overlap of the ranges of variation in all forms, little significance can be attributed to the difference in means of ferox and asper.
Fig. 13. Ratio of length of carapace to length of plastron (CL/PL) in some American species and subspecies of the genus Trionyx. Symbols as in Fig. 3. T. ferox has proportionately the shortest carapace.
Scalation
Cornified, smooth or cusplike areas occur on each limb, but their number and arrangement are of no taxonomic value. Normally, the anterior surface of each forelimb possesses four cornified areas for which the term antebrachial scales is proposed (Fig. 14). Two of the four scales occur in a more dorsal position; the lateral edge of the proximal one is free and cusplike along a part [465] of its length, whereas the distal scale is smooth-edged. Two scales having their lateral edges free and cusplike are ventral in position, and closer together than the two dorsad scales. Size of the scales and length of the free cusplike edges vary. Occasionally adjacent scales are fused or small additional scales are present. The number, configuration and arrangement of the two cornified areas on each hind limb are constant. One of these scales is smooth-edged and occurs posteriorly on the dorsal surface. The other scale, situated on the ventral surface posteriorly in the region of the heel and distal to the smooth-edged scale of the dorsal surface, has a pronounced, cusplike, free edge.
Fig. 14. Dorsal surface of right forelimb showing normal number and arrangement of antebrachial scales in American species of the genus Trionyx (T. spinifer hartwegi, KU 15932, × 3/4).
Choanal Papillae
This term refers to the papillate flaps of skin that project from the lateral borders of the internal nares. Webb and Legler (1960:23) noted their presence in softshells, and Parsons (1958) discussed their occurrence in sea turtles of the family Cheloniidae and in the testudinid subfamily Emydinae (1960). In preserved softshells the choanal papillae may extend laterally and partly cover the nares, or may be folded vertically against the lateral borders of the nares; in the latter position the papillae are easily overlooked. To my knowledge, choanal papillae occur in all American species and subspecies of soft-shelled turtles. The free edge of each narial flap shows various degrees of fimbriation. The fimbriated border is least developed (margin nearly entire) in T. muticus and most developed in T. ater and T. ferox. In ater at least, the anteriormost portions of the narial flaps seem wider than in the other forms and show a greater degree of fimbriation than the posteriormost parts. The choanal papillae are most easily observed in large specimens.
Skull
In general, there is less difference between the skulls of ferox and spinifer than between either of those species and muticus (Stejneger, 1944:10–11). Figure 15 shows the general differences in proportions of the skulls of spinifer and muticus; Plate 54 shows the skull of the holotype of Platypeltis agassizi (= T. s. asper), which is similar to that of ferox; Stejneger (op. cit.) provided labelled drawings of the skull of T. spinifer as well as photographs of skulls of other forms.
The total of 159 skulls examined by me include 80 of spinifer, 50 of ferox, and 29 of muticus. There are no secondary sexual differences between skulls of corresponding size, except in agassizi-form skulls mentioned under the account of T. s. asper, and possibly in ferox. Most, and possibly all, of the skulls of muticus having a basicranial length of 40.0 millimeters or more, and those of spinifer exceeding 50.0 millimeters must represent females (by correlation of known maximum size of males with greatest width of head, which is, in turn, compared with the greatest width of skull and corresponding basicranial length).
Fig. 15. Skulls of Trionyx spinifer hartwegi (left, a-d, KU 2757), and Trionyx muticus muticus (right, e-h, KU 1870). Dorsal views, a (× 1/2), e (× 3/4); occipital views, b (× 5/6), f (× 1); lateral views, c (× 1/2), g (× 3/4); ventral views, d (× 1/2), h (× 3/4).
a., alveolar surface of upper jaw
aq., articular surface of quadrate
ex., exoccipital
fp., fenestra postotica
fm., foramen magnum
if., intermaxillary foramen
ic., internal choana
mx., maxilla
mxb., maxillary bridge
oc., occipital condyle
op., opisthotic
ope., opisthotic-exoccipital spur
opw., opisthotic wing
pmx., premaxillaries (fused)
pt., pterygoid
q., quadrate
qj., quadratojugal
sq., squamosal
s., supraoccipital spine
tc., tympanic cavity
Measurements used include basicranial length (occipital condyle to tip of upper jaw), greatest width (variable in position), greatest width of alveolar surface of maxilla (taken at level immediately posterior to anterior margin of internal choanae), greatest length of internal choanae, and least breadth of maxillary bridge (separating internal choanae and intermaxillary foramen). One ratio developed from the measurements was greatest length of internal choanae/least breadth of maxillary bridge, hereafter referred to as IC/MB. This ratio is discussed under the account of T. s. asper.
Greatest Width
The position or level on the skull where the greatest width (Table 3) occurs is of some diagnostic value in distinguishing the skulls of ferox from spinifer and muticus. Skulls of ferox usually are widest at the level of the quadratojugal (immediately in front of tympanic cavity), whereas skulls of spinifer and muticus usually are widest slightly more posteriorly at a level on the squamosal immediately behind the tympanic cavity. Occasionally the width at the level of the quadratojugal and squamosal is the same, or the greatest width of skull may be ventrad between the quadrates, which are slightly flared laterally. The latter condition possibly is most prevalent in muticus.
Table 3. Variation in Position of Greatest Width of Skull of North American Species of the Genus Trionyx (excluding ater). The Number of Specimens Examined (in Parentheses) Follow the Specific Names.
| Position | Species | ||
| ferox (36) | spinifer (47) | muticus (14) | |
| Squamosal | 7 (19%) | 35 (74%) | 11 (79%) |
| Quadratojugal | 26 (72%) | 7 (15%) | 1 (7%) |
| Quadrate | 2 (6%) | ⋯ | 2 (14%) |
| Squamosal and quadratojugal of same width | 1 (3%) | 5 (11%) | ⋯ |
Supraoccipital Spine
The ventral surface of the supraoccipital spine in muticus lacks a medial ridge, and gradually increases in width anteriorly, so that it is widest proximally in the region of the roof of the foramen magnum. In ferox and spinifer, the ventral surface, usually having a medial ridge, is narrow and of the same width throughout its length or somewhat flared distally. The ventral surface of the supraoccipital spine, which is widest proximally in muticus, is always narrow proximally in ferox and spinifer. The ventral surface of the supraoccipital spine of one skull of spinifer, USNM 91311, differs little from that of muticus.
Foramen Magnum
The shape of the foramen magnum is generally rhomboidal in spinifer and ferox; the ventral angle is semicircular, the lateral angles obtuse, and the dorsal angle more acute. The shape of the foramen magnum in muticus is ovoid, higher than wide; the sides are evenly rounded.
Opisthotic-Exoccipital Spur
Skulls of spinifer normally have the fenestra postotica partly restricted by a medially-slanting, descending spur from the roof of the fenestra postotica; the spur incorporates the suture between the exoccipital and opisthotic and includes parts of those two bones. On one skull (KU 2824) the spur is displaced more medially and does not incorporate the opisthotic. The descending spur contacts the pterygoid ventrally forming a complete bony strut traversing the fenestra postotica in some skulls (KU 2228, 2666, 2762, TU 15423, MCZ 46621, TU 15415, right side only). The fenestra postotica on skulls of ferox and especially muticus is not normally restricted by an opisthotic-exoccipital spur.
Often the spur is reduced and indicated by a smooth projecting ridge. Sometimes the spur or ridge is absent on skulls of spinifer, and I have seen no well-developed spur on a skull of muticus. The development of the spur is not due to ontogenetic variation. There is some variation in development of the spur on either side of the skull; two skulls of ferox have the combination ridge/absent, and two of spinifer have the combinations ridge/spur and spur/absent. The frequency (based on counts of individual skulls) and the degree of development of the spur among the three species is indicated in Table 4.
Table 4. Frequency and Degree of Development of Opisthotic Exoccipital Spur of North American Species of the Genus Trionyx (excluding ater). The Number of Specimens Examined (in Parentheses) Follow the Specific Names.
| Development of Spur | Species | ||
| ferox (43) | spinifer (68) | muticus (29) | |
| spur (well-developed) | 1 (2%) | 45 (66%) | ⋯ |
| ridge (reduced) | 7 (16%) | 20 (30%) | 1 (3%) |
| absent | 35 (82%) | 3 (4%) | 28 (97%) |
Loveridge and Williams (1957:415, footnote) cited Siebenrock who mentioned a descending process of the opisthotic in Dogania (= Trionyx) subplana and Trionyx sinensis. I have not seen an ascending process of the pterygoids on skulls of American softshells as described by Loveridge and Williams (op. cit.:414, 429, fig. 54) for Lissemys, Cyclanorbis, Cycloderma and some Trionyx triunguis.
Opisthotic Wing
This term refers to the laterally directed, posterior part of the opisthotic that is visible in occipital, lateral and ventral views. In ventral view the opisthotic wing is most easily seen and is wider in muticus than in spinifer or ferox. In muticus the distal part is truncate, whereas in ferox and spinifer, it is more tapered and gently rounded, although somewhat unevenly flared [469] medially. Also there is more of a downward curvature (in ventral view) of the opisthotic wing in muticus than in ferox or spinifer; consequently the tip of the wing in muticus is often just visible in dorsal view (on lateral side of squamosal), certainly in lateral view. The distal part or tip of the opisthotic wing is not visible in dorsal view on skulls of ferox or spinifer.
Articular Surface of Quadrate
The ventral surface of the quadrate that articulates with the mandible is composed of a lateral condyle and a medial articular surface. The condyle and medial articular surface are separated by a furrow. On skulls of ferox and spinifer the lateral condyle, which is not conspicuously tapered posteriorly, is slightly larger than the medial articular surface, and the furrow is shallow. On skulls of muticus, the lateral condyle is conspicuously tapered posteriorly, is slightly smaller than the medial articular surface, and the furrow is deep.
Contact of Maxillaries Above Premaxillaries
The contact of the maxillaries above the premaxillaries is of diagnostic value in distinguishing skulls of ferox and spinifer from those of muticus. I have seen no skulls of muticus on which the maxillaries were in contact, and no skulls of ferox on which the maxillaries were separated. Stejneger (1944:19), however, reported a skull of muticus (USNM 102677) having the maxillaries in contact. Maxillaries are in contact (sometimes just barely) in 65 of 74 skulls of spinifer (88%); the premaxillaries are separated on nine skulls (12%).
Carapace
The dorsal surface of the bony carapace of American trionychids consists of a nuchal, seven or eight pairs of pleurals, and seven or eight, rarely nine, neurals (Fig. 16). The lateral parts of the nuchal overlie the second pair of ribs. The distal parts of the second through the ninth pair of ribs extend laterally beyond the lateral edges of the pleurals. There are no marginal ossifications. The posterior part of the bony carapace bears blunt, rounded or ovoid to linear, prominences mostly on the last pair of pleurals principally on large females of spinifer and ferox; I have seen only one adult male (stuffed, MCZ 46633) having a semblance of welts on the bony carapace. The nuchal, pleurals and neurals are sculptured.
As growth proceeds, the single, transversely-oriented, fontanelle of young turtles that separates the nuchal from the first neural and first pair of pleurals divides into two fontanelles that generally decrease in size and finally disappear. Occasionally only one (unilateral) large fontanelle is present (USNM 54734, muticus). The largest specimens noted that retain fontanelles are a ferox (USNM 029474) having a plastron 24 centimeters long, and a spinifer (USNM 54731) having a plastron 20 centimeters long. The fontanelles probably are present in some larger individuals.
Fig. 16. Carapace of Trionyx spinifer (a), and sketches of posterior parts of carapaces (b-i) of three American species, showing number and variation in arrangement of neurals and pleurals (not to scale; seventh neural, n7, and pleural, p7).
a. KU 2226, Lewisville, Lafayette County, Arkansas (× 1/3); sculpturing incompletely shown. Labels: r, ribs; nu, nuchal; n, neurals 1–7; p, pleurals 1–7.
b. ferox, USNM 60496, Auburndale, Polk County, Florida.
c. muticus, KU 1964, Doniphan Lake, Doniphan County, Kansas.
d. spinifer, USNM 100380, Plaquemine, Iberville Parish, Louisiana.
e. muticus, TCWC 7260, Red River, 8 mi. NW Ringgold, Montague County, in Clay County, Texas.
f. spinifer, USNM 59266, Homer, Winona, Minnesota.
g. muticus, KU 2840, White River, DeValls Bluff, Prairie County, Arkansas.
h. muticus, USNM 115939, Mississippi.
i. muticus, USNM 54734, Mississippi River, Fairport, Muscatine County, Iowa.
Most variation concerns the number of neurals and pairs of pleurals, and their arrangement posteriorly (H. M. Smith, 1947:121, table; Stejneger, 1944:18). Table 5 shows the frequency of occurrence of the number of neurals, pairs of pleurals, and the separation or contact of the seventh pair of pleurals; figure 16 illustrates some of the configurations of these plates posteriorly (e, g, and i not included in Table 5). The eighth pair of pleurals is reduced or absent (Loveridge and Williams, 1957:417). Eight neurals and eight pairs of pleurals occur in all three species. The seventh pleurals may contact each other in all three species, and their separation has been observed only in the species spinifer and muticus. Seven neurals and contact of the seventh pair of pleurals, or eight neurals and separation of the seventh pair of pleurals from each other occurs with approximately equal frequency in the species muticus. T. ferox and spinifer most often have seven neurals, seven pairs of pleurals, and the seventh pair of pleurals in contact. Stejneger (loc. cit.) mentioned a specimen in MCZ having nine neurals; I recorded nine neurals for USNM 54734 (Fig. 16i) for which Stejneger (loc. cit.) recorded eight. AMNH 57384 (ferox) has a small eighth pleural on the left side only, and USNM 115939 (muticus) has an eighth pleural only on the right side (Fig. 16h). Anomalous conditions observed included: an accessory bone between the first and second pleurals on the right side that contacts the first and second neurals in USNM 54733, (muticus); only six neurals in USNM 95193 (spinifer); a small accessory bony element between the first and second neurals in AMNH 57383 (ferox); and, only six pleurals (second and third fused) on the right side in USNM 54734 (muticus).
Table 5. Frequency of Occurrence of Number of Neurals, Pairs of Pleurals, and Separation or Contact of the Seventh Pair of Pleurals Among Species of American Soft-shell Turtles
| Number | Contact (+) or separation (-) of seventh pair of pleurals | Species | |||
| Neurals | Pairs of pleurals | ferox (16) | spinifer (60) | muticus (34) | |
| 7 | 7 | + | 9 (56%) | 50 (83%) | 13 (38%) |
| 7 | 8 | + | 5 (31%) | 2 (3%) | 2 (6%) |
| 8 | 7 | + | 2 (13%) | 3 (5%) | 3 (9%) |
| 8 | 8 | + | ⋯ | 4 (7%) | 2 (6%) |
| 8 | 7 | - | ⋯ | 1 (2%) | 14 (41%) |
Ventrally, the bony carapace shows ten thoracic vertebrae, the second through the ninth having well-developed, depressed ribs that are fused (no sutures) to the pleurals. The ribs of the first thoracic vertebra are represented by bony struts that extend posterolaterally and contact the anterior borders of the second pair of ribs. The two ribs of the ninth pair are free for most of their length and often are broken; they are slightly shorter than the eighth pair of ribs. The ribs of the tenth thoracic vertebra may be well-developed (KU 2219, 2666, 50856, spinifer, and 16528, ferox), but are usually broken off and represented only by transverse processes.
Kyphosis
Kyphosis (angular curvature of the vertebral column) or the hump-backed condition in American softshell turtles has been summarized by Nixon and Smith (1949:28). Cahn (1937:185, pl. 25e) illustrated the condition in an [473] individual of T. spinifer, and H. M. Smith (1947:119) mentioned kyphotic softshells representing the species spinifer (subspecies hartwegi and emoryi) and muticus. Neill (1951:10) mentioned two kyphotic T. s. asper and Nixon and Smith (loc. cit.) recorded the report of a kyphotic T. ferox. I have noted the condition in four muticus (subspecies muticus, KU 1959–60, 23230; INHS 2148) and seven spinifer (CNHM 22925; subspecies hartwegi, USNM 55689; subspecies spinifer, UMMZ 52948, 95615; subspecies emoryi, KU 2219, 33523, TU 16240). The smallest kyphotic specimen, a hatchling, TU 16240, has a plastral length of 3.5 centimeters. Kyphosis is to be expected in all kinds of softshells as are other abnormalities, such as albinism (reported for Lissemys by D'Abreu, 1928, and partial albinism noted in T. cartilagineus by Mohr, 1929) or congenital absence of limbs (reported by Dutta, 1931, as occurring in the genera Trionyx and Lissemys). The cause of kyphosis is not known. Smith (op. cit.:120) suggested an abnormally early fusion of the costals (= pleurals) with the ribs, and a subsequent differential rate of growth between them and the vertebral column as a hypothesis; Williams (1957:236) proposed that late retraction of the yolk mass, or retraction of an excessively large yolk mass may cause kyphosis. The cause of kyphosis may be of genetic origin or due to some environmental damage to the vertebral column prior to the cessation of growth. The variation in rate of growth of the vertebral column may produce humps of different shapes and sizes. Some of the specimens noted above (UMMZ 52948, 95615) have the carapace only slightly arched and are considered partly kyphotic. There seem to be degrees of kyphosis, a fact that should be taken into account in considering the occurrence of variation in greatest depth of shell.
Plastron
The plastron is united to the carapace by ligamentous tissue and is somewhat flexible anteriorly and posteriorly. Anteriorly the plastron is somewhat hingelike and may contact the anteriormost edge of the carapace. The bony elements are reduced. There is usually a median vacuity, which is relatively smaller in larger specimens and may be divided into two vacuities (a posteromedial and an anteromedial) by the medial juxtaposition of the hyo-hypoplastra, especially in muticus. Williams and McDowell (1952) have recommended a change in nomenclature for some of the plastral bones on the basis of reinterpretation of their homologies. The nine plastral bones include: an anterior pair of preplastra (= epiplastra, auct.); an unpaired, median bone, representing fused epiplastra (= entoplastron, auct.), hereafter referred to as the epiplastron; a pair of hyoplastra; a pair of hypoplastra; and, posteriorly, a pair of xiphiplastra (Fig. 17).
Siebenrock's (1902) synopsis of living trionychids was based entirely on plastral characters. He distinguished between muticus and spinifer principally by the shape of the epiplastron; T. ferox was not considered different from spinifer. The median angle formed by the boomerang-shaped epiplastron is obtuse and somewhat greater than 90 degrees in muticus (Fig. 17a); the angle of the epiplastron in spinifer and ferox is smaller than in muticus and forms an approximate right angle (Fig. 17b). Williams and McDowell (op. cit.:277, Pl. 1, Fig. 3) presented an illustration of the anterior plastral elements of an adult T. ferox. Siebenrock provided illustrations of the plastrons of muticus (op. cit.:823, Fig. 5) and spinifer (op. cit.:830, Fig. 10).
Fig. 17. Plastron of Trionyx muticus (a) and T. spinifer (b); sculpturing of callosities incompletely shown. ep, epiplastron; hp, hyoplastron; hyp, hypoplastron; pp, preplastron; xp, xiphiplastron. a—KU 1868, White River, Devall's Bluff, Prairie County, Arkansas (× 2/3); b—KU 1869, same locality (× 2/3).
Much importance has been credited to the fusion (no suture) or separation (suture present) of the hypoplastra and hyoplastra. The fusion of these bones distinguishes the genera Lissemys, Cyclanorbis and Cycloderma from Trionyx, Pelochelys, and Chitra (Siebenrock, op. cit.:815, 817; Loveridge and Williams, 1957:415). This character is also one of the criteria used by Hummel (1929: 768) in his erection of the two subfamilies Cyclanorbinae (= Lissemyinae) and Trionychinae. In my examination of specimens this character, unfortunately, was not given full attention. I have noted the fusion of the hypoplastra and hyoplastra in KU 1878 (muticus, right side only), KU 2219 (kyphotic spinifer), KU 16528 (ferox) and KU 60121 (ferox). Dr. Ernest E. Williams informs me in a letter of November 17, 1959, that of six specimens of ferox in the MCZ, the hyoplastra are fused with the hypoplastra in three (54689–90, 54686). I suspect that these bones in the three American species of the genus Trionyx, especially in ferox, fuse more often than is supposed.
In muticus the constricted part of the hyoplastron and hypoplastron is wider anteroposteriorly than in spinifer or ferox (Fig. 17).
The three American species have on the hyoplastra, hypoplastra, and xiphiplastra well-developed callosities, which enlarge with increasing size. The medial borders of the hyoplastral and hypoplastral callosities in larger specimens are rounded and closely approximated, often touching, as do the callosities of each xiphiplastron; seemingly, the callosities are relatively larger in muticus than in spinifer and ferox. I have seen one adult male muticus (KU 41380) that lacked median fontanelles or vacuities owing to the contact of the plastral elements (as viewed through overlying skin, alcoholic specimen). The bony plastron (approximately 9 cm. in maximal length) of a small muticus (KU 19460) resembles the plastron of larger individuals of muticus in having well-developed hyoplastral and hypoplastral callosities that are closely approximated medially. Large individuals of muticus usually have small, ovoid callosities on the preplastra, and a well-developed, angular callosity on the epiplastron (Fig. 17a). Siebenrock (op. cit.:823) suggests that the presence of callosities on the preplastra and epiplastron of muticus is subject to individual variation. I can not substantiate or dispute the supposition of Baur (1888:1122), Siebenrock (1924:193) and Stejneger (1944:12, 19) that the callosities are larger in males of muticus than in the females. Some individuals of spinifer have seven plastral callosities (KU 2842) as does muticus, but the callosities on the preplastra and epiplastron are less frequent and less well-developed in large specimens of spinifer than in muticus. The small epiplastral callosity in spinifer is located at the medial angle and does not extend posterolaterally to cover the entire surface of the epiplastron as it may in muticus (Fig. 17b). The epiplastron of a spinifer (KU 2826) has a medial callosity and another on the right posterolateral projection; three separate callosities occur on the epiplastron of MCZ 46615. The last specimen mentioned, a large, stuffed female, possesses a round, intercalary bone that tends to occlude the posteromedial vacuity. Seemingly, the callosity on the epiplastron appears prior to those on the preplastra; I have not seen any plastra having callosities on the preplastra and lacking a callosity on the epiplastron. I have not noted callosities on the preplastra or epiplastron of specimens of ferox.
The callosities on the plastral bones are sculptured; small, recently formed callosities on the preplastra and epiplastron lack sculpturing. The pattern [476] of sculpturing on the plastral bones as well as that of the carapace is generally of anastamosing ridges. I am unable to discern any differences in pattern of sculpturing between the three American species. Stejneger distinguished adult specimens of ferox from the other American species by the coarseness of the sculpture of the bony callosities (1944:24) and of the bony carapace (op. cit.:32). The sculpturing on the plastral callosities and carapace seems to be correlated with size; larger specimens (ferox) have coarser sculpturing than do smaller specimens (muticus). Stejneger also mentioned that the sculpturing on many specimens of ferox is specialized into prominent, longitudinal welts (loc. cit.); these welts occur also on the carapace of spinifer.
On the basis of the osteological characters examined by me, T. muticus is distinguished from spinifer and ferox by a number of characters (plastron and especially skull) whereas the species spinifer and ferox are not easily distinguished from one another.
Composition of the Genus Trionyx in North America
Analysis of the characters previously mentioned and their geographic distribution permits the recognition of ten taxa, comprising four species and eight subspecies. Two subspecies, T. spinifer pallidus and T. s. guadalupensis are described as new. The four species and the included subspecies here recognized are:
Trionyx ferox
Trionyx spinifer spinifer
hartwegi
asper
emoryi
guadalupensis
pallidus
Trionyx ater
Trionyx muticus muticus
calvatus
The following key is designed to permit quick identification of living individuals; therefore, ratios and osteological characters are avoided as much as possible in favor of other characters that are the least variable and most "typical." Because there is considerable variation correlated with sex and size, each taxon occurs in the key in more than one couplet. Large females having mottled and blotched patterns will be the most difficult to identify. The characters listed should be used in combination because one character alone may not be sufficient; it is advisable to read both choices of each couplet. The text, figures and illustrations should be consulted for final identification.
Artificial Key to North American Species and Subspecies of the Genus Trionyx
1. Septal ridges present; tubercles on anterior edge of carapace present or absent
2
Septal ridges absent; anterior edge of carapace lacking tubercles or raised prominences
19
2. Plastral area a uniform dark slate or blackish; soft parts of body blackish having large pale marks dorsally; carapace having large black blotches, often fused along margin, on pale background, and many well-defined longitudinal ridges
T. ferox, p. 479
Combination of characters not as above; ventral surface whitish, blackish flecks or blotches sometimes present
3
3. Carapace having pattern of white dots, or black ocelli and/or spots; carapace sometimes gritty resembling sandpaper
4
Carapace uniform pale brownish or grayish, or having mottled and blotched pattern, contrasting or not; white dots or tubercles, black ocelli and/or spots may be present; carapace not gritty
10
4. Carapace having pattern of black ocelli and/or spots; numerous, conspicuous whitish spots or tubercles absent
5
Carapace having pattern of white dots that are sometimes surrounded by small black ocelli; small black dots may be interspersed among larger white dots
7
5. Carapace having two or more marginal lines, these often diffuse and interrupted; black spots sometimes ocellate or bacilliform, or interspersed among smaller black dots; postocular and postlabial stripes usually united
spinifer asper, p. 502
Carapace having only one dark marginal line; pattern of black ocelli or spots; postocular and postlabial stripes usually not united
6
6. Carapace having prominent ocelli, which are much larger near the center than at the sides
spinifer spinifer, p. 489
Carapace having numerous small, dark spots, sometimes small ocelli, which are not much larger near the center than the sides
spinifer hartwegi, p. 497
7. White spots on anterior third of carapace; white spots on carapace often surrounded by narrow blackish ocelli; small black dots sometimes interspersed among white spots
spinifer guadalupensis, p. 517
White spots absent on anterior third of carapace, or small and inconspicuous; white spots not surrounded by narrow blackish ocelli
8
8. Pale rim of carapace narrow, partly obscured; over-all dorsal coloration (including soft parts of body) dark and lacking pattern; few, small, white tubercles confined to posterior third of carapace
ater, p. 528
Pale rim distinct, without markings; soft parts of body dorsally not uniformly dark; many white tubercles usually contrasting on pale carapace
9
9. White spots confined to posterior third of carapace; ground color of carapace usually pale brown or tan, sometimes darker; a dark, slightly curved, line connecting anterior margins of orbits; postocular stripe usually interrupted leaving pale, blotch behind eye; pale rim of carapace four or five times wider posteriorly than laterally
spinifer emoryi, p. 510
Small white spots on posterior half of carapace gradually decreasing in size anteriorly, often indistinct or absent on anterior third of carapace; pale rim of carapace no more than three times wider posteriorly than laterally
spinifer pallidus, p. 522
10. Marginal ridge present; carapace having ill-defined dark blotches on uniform grayish, lacking whitish tubercles or well-defined black spots or ocelli; pale rim of carapace absent; tubercles on anterior edge of carapace resembling flattened hemispheres; anterior parts of plastron often visible in dorsal view; postocular stripe, if present, having thick, blackish borders
ferox, p. 479
Marginal ridge absent
11
11. Carapace uniform pale brownish, lacking mottled and blotched pattern, white dots, black ocelli or spots
12
Carapace having mottled and blotched pattern, contrasting or not; white spots or tubercles, black ocelli or spots may be present
13
12. Pale rim of carapace four or five times wider posteriorly than laterally; dark, straight or slightly curved, line connecting anterior margins of orbits
spinifer emoryi, p. 510
Pale rim of carapace no more than three times wider posteriorly than laterally
spinifer pallidus, p. 522
13. Rear margin of carapace usually roughened by fine corrugations, edge often ragged; pale rim absent; carapace having dark brown-blackish, mottled and blotched pattern; anterior edge of carapace more or less smooth having scarcely elevated prominences; posterior part of plastral area and especially ventral surface of carapace having numerous black marks
ater, p. 528
Rear margin of carapace smooth, edge entire; usually some evidence of pale rim
14
14. White, rounded tubercles or spots usually evident posteriorly on carapace, sometimes indistinct; black ocelli or spots lacking in center of carapace, sometimes present at sides; shape of tubercles on anterior edge of carapace variable
15
White spots or tubercles absent; margin of carapace usually having black ocelli or spots; tubercles on anterior edge of carapace equilateral or conical, not low and flattened
17
15. White spots often present on anterior half of carapace; tubercles on anterior edge equilateral and wartlike, or less elevated, not conical
spinifer guadalupensis, p. 517
White spots usually absent on anterior half of carapace, sometimes indistinct; shape of tubercles on anterior edge of carapace variable
16
16. White spots absent on anterior half of carapace; tubercles on anterior edge of carapace low, scarcely elevated, never equilateral or conical; mottled and blotched pattern often not contrasting; ground color of carapace sometimes dark; pale rim of carapace four or five times wider posteriorly than laterally; dark, straight or slightly curved, line connecting anterior margins or orbits
spinifer emoryi, p. 510
White spots sometimes indistinct on carapace, or few, small spots present on posterior half of carapace; tubercles on anterior edge of carapace equilateral and wartlike or conical; mottled and blotched pattern usually contrasting; pale rim less than three times wider posteriorly than laterally
spinifer pallidus, p. 522
17. Carapace having evidence of more than one dark marginal line, and scattered, black spots or ocelli
spinifer asper, p. 502
Carapace having only one, dark, marginal line
18
18. Carapace having small black spots, lacking large interrupted ocelli
spinifer hartwegi, p. 497
Carapace having small black spots interspersed among larger, interrupted ocelli
spinifer spinifer, p. 489
19. Carapace having pattern of dusky spots, sometimes short lines
20
Carapace lacking pattern of dark spots or lines, having a mottled and blotched pattern
21
20. Pattern of circular spots, lacking short lines or bacilliform marks; spots sometimes slightly ocellate; no pale stripes on snout
muticus calvatus, p. 539
Pattern of dots, or dots and short lines; pale stripes on snout, at least just in front of eyes
muticus muticus, p. 534
21. Mottled and blotched pattern usually contrasting; ill-defined, blackish blotch absent behind eye
muticus muticus, p. 534
Mottled and blotched pattern usually not contrasting; ill-defined, dark blotch may be present behind eye
muticus calvatus, p. 539
Systematic Account of Species and Subspecies
Trionyx ferox (Schneider) Florida Softshell
Plates 31 and 32
Testudo ferox Schneider, Naturg. Schildkr., p. 330, 1783 (based on Pennant, Philos. Trans. London, 61 (Pt. 1, Art. 32): 268, pl. 10 [figs. 1–3], 1772).
Trionyx ferox Schwartz, Charleston Mus. Leaflet, No. 26:17, pls. 1–3, May, 1956.
Testudo mollis Lacépède, Hist., Nat. Quadr. Ovip. Serp., 1:137, pl. 7, 1788.
Testudo (ferox?) verrucosa Schoepff, Hist. Testud., Fasc. 5 (Plag. M):90, pl. 19, 1795.
Testudo bartrami Daudin, Hist. Nat. Rept., 2:74, pl. 18, fig. 2, 1801.
Trionyx georgicus Geoffroy, Ann. Mus. Hist. Nat., Paris, 14:17, August, 1809.
Mesodeca bartrami Rafinesque, Atlan. Jour., Friend Knowledge, Philadelphia, 1 (No. 2, Art. 12):64, Summer, 1832.
Trionyx harlani Bell in Harlan, Medic. Phys. Research, p. 159, 1835.
