OF THE FAMILY BACILLARIA. 155 



PODOSPHENIA. 



Carapace simple , siliceous, cuneiform, fixed ivhen young- hy 

 one end, afterwards often free, longer than broad, pedicel small, 

 hemispherical, or wanting: 



In PL III, fig. 3, is represented a species which agrees with the 

 above generic characters, and which I therefore place here, al- 

 though it is a fiuviatile production, while all of Ehrenberg's spe- 

 cies are marine. It invests stones, &c. in small streams near 

 West Point with a yellowish green covering, which appears lilce 

 a mere stain, but which when scraped ofTwith a knife, is seen to 

 be composed of excessively minute frustules resembling those of 

 Gomphonema, but which have no perceptible pedicel. 



GOMPHONEMA. 



Carapace simple, siliceous, cuneiform, fixed upon a distinct 

 filiform, branching pedicel, dichotomous by spontaneous division. 



1. Gomphonema nninutissimmn. (PL III, fig. 4.) Smooth ? corpus- 

 cles cuneiform, curved, clavate, -^\-^ to y'^- of ^ ^ii^®- 



A minute species agreeing closely with Kutzing's figure of G. 

 minutissimum, (see Linnea, 1833, fig. 43,) occurs abundantly on 

 various aquatic plants in the Hudson River at West Point. It 

 varies much in size ; fig. 4, a, shows the largest individuals, and 

 fig. 4, b, the smaller ones. 



2. Gomphonema . (PL III, fig. 5, a, b.) This large and beau- 

 tiful species appears to be related to G. dichotomum and to G. gemi- 

 nation, but I am unable to satisfy myself of its identity with either. 

 I found it in vast quantities at the Island of Mackinaw, Straits of 

 Michilimackinac, on a large cedar tree which was sunk in water ten 

 or fifteen feet deep, and which was literally covered with large 

 waving bunches of a yellowish white color, composed of the dicho-_ 

 tomous filaments of this species, glittering with crystal-like particles. 



The individuals are striate, with one side cuneate, and show- 

 ing at the broad end two interior arcuate folds ; the Qther side is 

 elongated, obovate or clavate, with a central circular spot and lon- 

 gitudinal smooth portion. The pedicel is repeatedly dichoto- 

 mous. 



