Читать книгу The Diatomaceæ of Philadelphia and Vicinity - Charles S. Boyer - Страница 25

(coscinon, a sieve, and discus)

Frustules solitary, cylindrical, compressed; valve circular or elliptical; surface flat or sometimes convex near the border; markings more or less angular, radiating, sometimes fasciculate; border usually well defined. Central space, if present, hyaline, sometimes surrounded with a rosette of large cells.

Chromatophores round, angular or irregular discs usually without pyrenoids (Karsten).

Rattray's classification is here followed, so far as it refers to our species.

Excentrici.—Valves circular; central space absent; markings angular, in oblique, decussating rows.

Lineati.—Central space absent; markings angular, oblique decussating rows straight.

Fasciculati.—Markings fasciculate, or sometimes only near the border.

Radiati.—Markings rounded or angular, more or less radiate.

Elaborati.—Valves elliptical, markings rounded.

EXCENTRICI

COSCINODISCUS EXCENTRICUS EHR.

Valve with a hyaline excentric space from which proceed, usually in six directions, rows of polygonal markings decreasing toward the narrow, coarsely striated border, the rows appearing convex toward the centre. Apiculi at unequal distances apart. Quite variable in size.

Common in the blue clay and along the coast.

Pl. 2, Figs. 14 and 20.

Fig. 20 is probably var. perpusilla Grun. (Diat. Fr. Jos. L., Pl. 4 (D), Fig. 7).

LINEATI

COSCINODISCUS LINEATUS EHR.

Valve circular, markings hexagonal, cells in parallel rows. Border narrow, cellular.

Blue clay and Atlantic coast. Not common.

Pl. 3, Fig. 8.

FASCICULATI

COSCINODISCUS NITIDUS GREG.

Valve flat, markings rounded, distant, radiate, decreasing toward the border which is coarsely striate. Quite variable in size and in the distance between the markings.

Blue clay and Atlantic coast. Common.

Pl. 2, Fig. 18.

COSCINODISCUS NITIDULUS GRUN.

Valve usually not quite circular; markings smaller than in nitidus and fasciculate near the border.

Blue clay.

Pl. 2, Fig. 19.

Various intermediate forms between nitidus and nitidulus occur.

COSCINODISCUS SUBTILIS EHR.

Markings polygonal, irregular at the centre, but forming numerous fasciculi radiating toward the border, the rows parallel to the central row of each fasciculus. Border narrow with fine striæ; apiculi often present between the fasciculi.

Blue clay and along the coast. Very common in the water supply of Philadelphia and Camden, where the diameter seldom exceeds 40 µ and the markings on the semi-radius are 10 in 10 µ.

Pl. 2, Fig. 17.

COSCINODISCUS DENARIUS SCHMIDT

Markings larger than in C. subtilis, equal, forming usually ten fasciculi, each beginning near the semi-radius and containing ten parallel rows of granules.

Common in the blue clay and sparingly along the coast.

Pl. 2, Fig. 13.

Forms are found intermediate between C. subtilis and C. denarius, as shown in Fig. 15.

COSCINODISCUS POLYACANTHUS GRUN.

Markings angular, 10 in 10 µ, decreasing toward the border, fasciculate. Apiculi large, twelve or more, usually inserted at the middle of each fasciculus, and extending into the interior of the cell. The apiculi in outline resemble the heads of horse-shoe nails, and are seen with difficulty except when the valve is examined from the inner side. Border narrow, striated. Diam. 70 µ.

Pensauken, N. J., artesian well.

Pl. 38, Fig. 5.

Rattray's description of C. polyacanthus var. intermedia Grun., from Cape Wankarema, Siberia, gives the diam. as 60 µ, and there are about 7 markings by actual count in 10 µ in Grunow's figure (Diat. Fr. Jos. Land, Pl. 3 (C), Fig. 25). The apiculi are more numerous, but there appears to be little doubt of the general similarity. The Philadelphia form is abundant in the Pensauken well deposit at a depth of 33 ft. The apiculi become quite distinct in slides stained with silver nitrate by Mr. F. J. Keeley; they are distinct from small apiculi sometimes evident between the fasciculi. The specimens in the Pensauken deposit are mingled with other forms which cannot be distinguished from C. subtilis. Whether the two are identical, I am unable to determine. Rattray (Rev. Cos., p. 47) refers to H. L. Smith's Type Slide No. 100, from rice-field mud, Savannah, Ga., as C. subtilis. In Smith's slide, in my possession, a number of the forms show faint outlines of the large apiculi and are otherwise exactly like C. polyacanthus.

RADIATI

COSCINODISCUS VELATUS EHR.

Markings angular, decreasing slightly toward the coarsely striated border, covered with fine puncta.

Blue clay.

Pl. 3, Fig. 2.

COSCINODISCUS MARGINATUS EHR.

Markings rounded, large, decreasing toward the broad border, which is coarsely marked with distant striæ. The cells are punctate.

Common in the blue clay.

Pl. 3, Fig. 9.

In the fossil forms the puncta are not evident, hence the species is usually described as not punctate.

COSCINODISCUS RADIATUS EHR.

Markings polygonal, slightly decreasing toward the border where they are much smaller; border well marked, striate. Quite variable in size.

Common in the blue clay and along the coast.

Pl. 3, Fig. 11. Fig. 1 is probably a smaller form.

COSCINODISCUS SUBAULACODISCOIDALIS RATTR.

Markings small, decreasing toward the border in somewhat fasciculate rows. About one-third the distance from the border are five (Rattray finds six) well-marked apiculi somewhat resembling those of Aulacodiscus. Border narrow, hyaline.

Rare in the lower stratum of the blue clay.

Pl. 3, Fig. 4.

COSCINODISCUS ARGUS EHR.

Markings angular with central dots, increasing from the centre toward the border, where they are smaller.

Blue clay.

Pl. 3, Fig. 7 (a small form).

COSCINODISCUS BIANGULATUS SCHMIDT

Central space and rosette absent, markings large, angular, not punctate, with large central papillæ, decreasing toward the border. Border wide, coarsely marked with rows of granules, and with two indentations on the inner side distant from each other about two-thirds of the diameter.

Blue clay.

Pl. 3, Fig. 3.

Distinguished from Coscinodiscus asteromphalus var. omphalantha Grun., which also has two constrictions, by the absence of punctate markings.

COSCINODISCUS ASTEROMPHALUS EHR.

Central space small, surrounded by a rosette of large polygonal cells from which radiate hexagonal cells, increasing about half way toward the border and then slightly decreasing. Cells punctate.

Blue clay.

Pl. 2, Fig. 16; Pl. 40, Fig. 12.

COSCINODISCUS ASTEROMPHALUS VAR. OMPHALANTHA (EHR.) GRUN.

Central space absent, rosette evident. Markings 2½ in 10 µ, somewhat smaller near the rosette and decreasing near the border, which is constricted in two places, as in C. biangulatus.

Blue clay.

Pl. 38, Fig. 10.

COSCINODISCUS OCULUS-IRIDIS EHR.

Central space and rosette distinct; markings polygonal, not punctate, with large papillæ, smaller near the rosette, increasing toward the semi-radius, and then decreasing to the striated border which is comparatively narrow.

Blue clay and Atlantic coast.

Pl. 3, Fig. 10.

ELABORATI

COSCINODISCUS LEWISIANUS GREV.

Valves elliptical, major axis a little more than twice the minor. From a point, usually near one side, radiate rows of granules in lines nearly parallel to the major axis. Border broad, with distinct striæ.

Great Sedge Island, N. J. (artesian well), and in outcrops later than the Miocene, where it is usually found.

Pl. 3, Fig. 5.