Sketch of the Infusoria of the family Bacillaria. 325 



boat-shaped frustules of Cocconeraa will generally serve to iden- 

 tify them. 



1. Cocconema , (PL 3, fig. 10.) Carapace lanceolate, ends 



obtuse, pedicels repeatedly dichotomous, secondary branches articula- 

 ted to the primary ones. Striae were not perceived. 



Abundant in the Hudson River at West Point. It appears to 

 be allied to C. lanceolatum of Agardh. 



2. Cocconema . (PI. 3, fig. 11, a, b.) These figures repre- 

 sent two positions of a species of Cocconema which is very common in 

 the living state near West Point, and which also abounds as a fossil. 

 In the living state I have but rarely seen it attached to a pedicel. It is 

 generally free, and moves about spontaneously like a Navicula. 



I once, on a cold day in October, noticed vast collections of this 

 species which were enveloped in a mucous covering, and which 

 formed large cloud-like masses several inches in extent, investing 

 aquatic plants, stones, &c. Each of these masses was crowded 

 with millions of the siliceous shells of this species. 



Ehrenberg mentions C. asperum as a new species detected by 

 him among the fossils from West Point. I am ignorant of its 

 distinguishing features. 



ACHNANTHES. 



Carapace simple, bivalve, or multivalve, siliceous, prismatic, 

 longer than broad, fixed by one end, pedicellate, pedicel oblique, 

 ventral, always simple, opening in the Tniddle of the body. Groups, 

 resulting from increase by spontaneous longitudinal division, re- 

 sembling chains, little banners, plates or ribboris. 



Achnanthes hrevipes. (PI. 3, fig. 12.) Corpuscles striate, curved 

 in the middle, ends rounded on the dorsal and ventral sides ; pedicel 

 thick, shorter than the body. 



I first noticed this species on filaments of Conferva fracta from 

 Providence Cove, R. I., and have since found it abundant on ma- 

 rine Algffi from Stonington, Conn. Small specimens, differing I 

 believe in no essential character, are also very abundant on aquatic 

 plants in the Hudson River at West Point. 



The Achnanthes longipes of authors may be a distinct species, 

 but the distinction " pedicel longer than the body," appears to me 

 to be founded on a character liable to much variation. I saw spe- 

 cimens at Stonington having pedicels much longer than the body, 

 yet they appeared to me to agree with E. brevipes in every other 

 respect. 



