OF THE FAMILY BACILLARIA. 157 



ton, Enteromorpha, &c. It agrees in many respects with E. 

 fulg-ens, Grev., but that is described as being striate, a character 

 which I have not perceived on our species. 



COCCONEMA. 



Carapace simple, bivalve or muUivalve, siliceous, fixed by one 

 end, pedicellate, longer than broad, pedicel in the direction of the 

 axis of the body. [Pedicellate Navicidce.) 



When separated from their footstallvs, there is no good charac- 

 ter to distinguish them from Navicula; but the unsymmetrical 

 boat-shaped frustules of Cocconema will g-enerally serve to 

 identify them. 



1. Cocconema . (PI. Ill, fig. 10.) Carapace lanceolate, ends 



obtuse, pedicels repeatedly dichotomous, secondary branches articu- 

 lated to the primary ones. Striae were not perceived. 



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

 be allied to C. lanceolatimi of Agardh. 



2. Cocconema . (PL III, 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 midtivalve, siliceous, prismatic, 

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

 ventral, ahvays simple, opening in the middle of the body. Groups, 



