74 
GEOLOGY OF THE FIRST DISTRICT. 
Eunotia. Free, single or binary; carapace simple, bivalve or muUivalve [siliceous) prismatic; four 
openings on the same side, two at each end, ventral side flattened, back convex and often dentate, ' 
never catenate by perfect spontaneous division. 
Eunotia arcus. (PI. 22, fig. 26, a, b.) Striate, carapace semi-lanceolate, elongated, two terminal knobs 
arcuate, 11 striae in line. 
Ehrenberg mentions E. arcus as occurring among fossil infusoria from West-Point. I 
presume that our figure, which represents a form very common both in the recent and fossil 
state in the United States, belongs to this species, 
Eunotia diodon. (PI. 22, fig. 29.) Striate, carapace elongated, ventral side flattened, slightly bidentate 
at the middle of the back, 19 striae in line, Jy to -yV hne. 
Hab. West-Point, fide Ehrenberg. Probably the same as fig. 29, which is common both 
recent and fossil at West-Point, and elsewhere in the United States, 
Eunotia tetraodon. (PI. 22, fig. 31.) Striate, carapace semi-lunar, short, flattened or concave on the 
ventral side, four rounded teeth on the convex back, 23 striae in yiy line, g’g to y’j line. 
Common among fossil infusoria from Manchester, Mass., and West-Point, N. Y. The 
living species occurs at West-Point. 
Eunotia pentodon. (PI. 22, fig. 32.) Striate, carapace semi-lunar, short, five teeth on the convex back, 
23 striae in yiy line. 
Fossil at Manchester, Mass, Living at West-Point. 
Eunotia serra. (PI. 22, fig. 33.) Striate, carapace linear, slightly curved, twelve to thirteen rounded 
teeth on the convex back, 19 striae in yiy line, y’y to Jy of a line. 
Our figure is from specimens found fossil in Massachusetts. 1 have also received it from 
various other localities. 
I strongly suspect that the number of the teeth on the back of the four last described spe¬ 
cies of Eunotia is liable to variation, and that the number of species has in consequence been 
made too great. (See remarks in Final Report on Geology of Massachusetts, Vol. II. p. 310, 
et seq.) 
Eunotia -. (PI. 22, fig. 27, a, b.) This species was found in water from a brackish ditch in New- 
Jersey, which was sent to me for examination by Dr. Torrey. It is concave on one side, convex 
on the other, with a slightly elevated and widened portion in the middle. It is also minutely striate. 
CoccoNF.Ts. Free, single, carapace simple, bivalve [siliceous), prismatic or hemispherical, a single open¬ 
ing in the middle of both sides of each carapace (?), never double or catenate by spontaneous 
division. 
Cocconeis? (PI. 22, fig. 31.) Represents what I believe to be a species of Cocconeis. I found it ad¬ 
hering to a small marine Alga from the eastern shore of Florida. 
Beautiful figures of Cocconeis ( Campylodiscus) clypeus, drawn by F. Bauer, will be found 
in Pritchard’s Hist. Inf., PI. 12, fig. 516 - 518. I have received fine specimens of these ele¬ 
gant fossils from E. J, Quekett, Esq. of London. 
Bacillaria. Free, [never fixed); carapace simple, bivalve or multivalve [siliceous), prismatic, 
forming chains or zigzag polypidoms by imperfect spontaneous division of the carapace and 
perfect division of the body. 
