Sketch of the Infusoria of the family Bacillaria. 323 



This species presents many points of resemblance both to Sy- 

 nedra ulna and Fragiilaria rhabdosoma of Ehrenberg, but I can- 

 not identify it positively with either. 



PODOSPHENIA. 



Carapace simple, siliceous, cuneiform, fixed when young hy 

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

 hemispherical, or ivanting. 



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

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

 though it is a fluviatile 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 like 

 a mere stain, but which when scraped off with 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 minutissimum. (PI. 3, fig. 4.) Smooth? corpus- 

 cles cuneiform, curved, clavate, -jiis *^ ^zline. 



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

 minutissimum, (seeLinnea, 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. Gomphonetna . (PL 3, fig. 5, a, i.) This large and beau- 

 tiful species appears to be related to G. dicbotomum and to G. gemina- 

 tum, 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 Michilli- 

 mackinac, 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 dichotomous 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 other side is 

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

 gitudinal smooth portion. The pedicel is repeatedly dichotomous. 



3. Gomphonema acuminatum? (PL 3, fig. 6.) Striate, corpuscles 

 elongated, wedgeform, end swollen and pointed, contracted on the side. 



