Читать книгу The Diatomaceæ of Philadelphia and Vicinity - Charles S. Boyer - Страница 17

(melos, a limb or member, and seira, a chain)

Frustules globose, ellipsoidal or cylindrical, concatenate, closely joined together. Valve either simply punctate or punctate and areolate. A constriction of the cell-wall, forming a furrow between the edge of the valve and the girdle, is more or less evident.

The genus Meloseira constituted by Agardh has been variously modified by Kuetzing, Thwaites, Wm. Smith, Van Heurck, De Toni, and others. In Systema Algarum Agardh included certain species of Conferva, of Lyngbye, Dillwyn and others, and limited his genus to frustules more or less globose (fila articulata ad genicula constricta), although in his Conspectus Criticus (p. 64), he modifies the description (fila teretia articulata, articulis diametro æqualibus vel longioribus) to include M. varians. As, however, Lysigonium Link, Gaillonella Bory, and other genera enlarged by Ehrenberg and Kuetzing, came to be included under Meloseira, Thwaites suggested the division of the genus into two: Orthosira, in which the frustules are not convex at the ends and Aulacosira in which no central line is apparent but with two distinct sulci. Wm. Smith adopts the genus Orthosira but rejects Aulacosira, including all forms under the former genus and Meloseira, suggesting that differences "exist in the formation of the sporangia" of the two genera. M. varians and M. crenulata appear to form auxospores or sporangial frustules in different ways, as will be noticed hereafter.

As, however, the present state of our knowledge is so limited and as much confusion would result in further changing the nomenclature, I shall adopt, for the most part, the division made by De Toni, separating Gaillonella and Lysigonium and employing the name Meloseira as emendated in Sylloge Algarum, although, as stated, it omits the species of Agardh. That a further division may be necessary is indicated by the differences existing between the Orthosira forms and the others.

ANALYSIS OF SPECIES

Frustules cylindrical and lengthened:
Valves with two distinct furrows; granules small	distans
Valves with coarse granules	granulata
Valves denticulate on the margin	crenulata
Valves denticulate and constricted	roeseana
Valves with row of large puncta on the girdle side	undulata
Frustules cylindrical and compressed:
Valves punctate and areolate	sulcata

The chromatophores consist of circular and compressed or irregular flat granules which lie along the wall of the cell.

MELOSEIRA DISTANS (EHR.) KUETZ.

Frustules cylindrical, slender, with two furrows, one on each side of the suture; valve in zone view with fine puncta in longitudinal rows; puncta in valve view scattered. L. 7-10 µ.

Meloseira nivalis Wm. Sm.

Coscinodiscus minor Wm. Sm.

Fresh water. Fossil in New England deposits.

Pl. 1, Figs. 8 and 9.

Note.—In all species of Meloseira, as well as Gaillonella and Lysigonium, the frustules are so closely coherent that when the filaments are broken entire frustules are less frequently found than a union of two valves of contiguous frustules.

MELOSEIRA GRANULATA (EHR.) RALFS

Frustules cylindrical, robust, 5-18 µ in diam., with large granules in longitudinal, sometimes spiral, lines, variable in size and arrangement in the same filament. Valve in valve view with scattered puncta. Variable in relative width and length, passing to M. crenulata.

Gaillonella granulata Ehr.

Orthosira punctata Wm. Sm.

Fresh water. Fossil at Coldspring, L. I.

Pl. 1, Fig. 10.

MELOSEIRA CRENULATA (EHR.) KUETZ.

Frustules cylindrical, with furrows on each side of the suture, 10-20 µ in diam.; puncta in longitudinal rows. Margins of valves denticulate at the junction of the frustules; valves with puncta scattered at the centre, radiate at the circumference.

Common in fresh water; quite variable in size.

Gaillonella crenulata Ehr.

Orthosira orichalcea Wm. Sm. in part; not Conferva orichalcea. Mertens or Gaillonella aurichalcea Ehr. and Bailey.

Pl. 1, Figs. 1 and 2.

MELOSEIRA ROESEANA RAB.

Frustules cylindrical, constricted toward each end, with coarse, longitudinal striæ; valve convex, striæ punctate, radiating, with several large granules at the centre. Connective zone with longitudinal rows of fine puncta. Diam. 12-45 µ.

Orthosira spinosa Grev.

Fresh water. Media, Pa. (Palmer); not common.

Pl. 1, Figs. 5 and 6.

MELOSEIRA ROESEANA VAR. EPIDENDRON (EHR.) GRUN.

Frustules denticulate at the margin; valve with coarse granules at the centre from which radiate lines of fine puncta.

Wet rocks of the Wissahickon.

Pl. 1, Figs. 3 and 4.

MELOSEIRA UNDULATA (EHR.) KUETZ.

Frustules single or in twos, usually broader than long, constricted near the margin. Valve with six to twelve internal projections forming with the outline of the constriction of the valve a polygonal figure within the circumference. Surface of the valve with radiating lines of puncta disappearing toward the centre, at which are numerous coarse puncta.

Meloseira gowenii A. Schmidt.

Blue clay of Philadelphia, especially common at Twelfth and Market Sts.

Pl. 1, Figs. 15, 16, 17.

MELOSEIRA SULCATA KUETZ.

Frustules quite robust, with diam. several times the length, deeply furrowed at the margin, areolate and punctate. Valve with radiating striæ disappearing toward the centre, and with a double row of cells near the margin, the outer one having the appearance of a crown of teeth.

Gaillonella sulcata Ehr.

Paralia sulcata (Ehr.) Cleve.

Paralia marina Heib.

Marine and brackish. Common in all parts of the world, and fossil in the Miocene. The Philadelphia form is the var. genuina Grun.

Pl. 1, Figs. 11 and 12.

In a gathering from Media of Meloseira crenulata (Palmer leg.), occasional filaments are noticed with much longer and narrower frustules which become enlarged in the middle and are seen to contain inner frustules in the process of still further division, as shown in Fig. 2, Pl. 38.

Meloseira dickei Thwaites shows internal box-like cells placed one within the other, which were supposed by Thwaites to be a method of reproduction. Wm. Smith doubts this, but is unable to offer any explanation. In the present form the mode of reduplication is that usually found in filamentous forms, but in this case the presence of perfect frustules enclosing others in the process of still further division has been heretofore unfamiliar to me. The swelling in the middle appears to indicate that not all filamentous diatoms are reduced in size by subdivision. In outline the valve is like that of a "truncated cone," as described by Petit in referring to Gaillonella granulata var. bambusina Petit (Diat. Nouv. et Rares, Jour. de Micrographie, 1890).