of the family Bacillaria. 323 
This species presents many points of resemblance both to Sy- 
nedra ulna and Fragillaria rhabdosoma of Ehrenberg, but I can- 
not identify it positively with either. 
PoposPHENIA. 
lecapens simple, siliceous, cuneiform, fixed when young by 
one end, afterwards often free, longer than broad, pedicel small, 
hemispherical, or wanting. 
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 
alg branching pedicel, dichotomous . spontaneous division. 
iphonema minutissimum. (Pl. 3, fig. 4.) Smooth? corpus- 
sig cuneiform, curved, clavate, ;}; to 7, lin Ans 
A minute species agreeing closely with itaing’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 siuiiler ones. 
2. Gonglohona (Pl. 3, fig. 5, a,b.) This large iad beau- 
tiful species appears to be related to G. dichotomum and to G. gemina- 
tum, but Iam 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, witha central circular spot and lon- 
a. smooth portion. The pedicel is repeatedly dichotomous. 
3. Gomphonema acuminatum? (PI. 3, fig. 6.) Striate, corpuscles 
siege, spsdgesaen, end swollen and pointed, contracted on the side. 
