296 Sketch of the Infusoria of the family Bacillaria. 
pearl-like appearance of these projections, when seen on the 
empty carapace, may have suggested the specific name. I have 
seen this species move quite distinctly, and have also seen in it 
(as well as other species of Euastrum) groups of moving mole- 
cules as in Closterium, sometimes indeed the whole cavity is fill- 
ed with such particles. Meyen states that the species he repre- 
sents (L. c. fig. 31, Pl. 10) contains globules of starch. 
This species is very common in the neighborhood of West 
Point. Ionce found, in the spring of the year, in a small pool 
caused by the melting of snow in a peat meadow, a large cloud- 
like mass in the water, which when touched, broke to pieces and 
became diffused through the water. On examination, it proved 
to be wholly made up of this species. I have found it in Rhode 
Island, New York, Ouisconsin, and Virginia. 
9. Euastrum (Fig. 9, Pl. 1.) Binary, triangular, angles 
rounded, each corpuscle having several rows of minute points. Hab. 
West Point. 
10. Euastrum (Fig. 10, Pl. 1.) Binary, elliptical, each 
corpuscle having three pairs of long subulate spines. Hab. West Point. 
I have met with individuals having the spines developed on only one side. 
ll. Euastrum (Fig. 13, Pl. 1.) Binary, corpuscles cor- 
date at base, each having six pairs of short spines. 
This is a very pretty species which occurs at West Point. The 
figure shows the position of two groups of active molecules. 
12. Euastrum — (Figs. 11 and 12, Pl. 1.) Binary, each cor- 
puscle elliptical and terminating at each extremity in a single spime- 
Hab. West Point. 
18. Euastrum (Figs. 2, 3, 4, 5, 6, and 7, Pl. 1.) Binary, 
(sometimes quaternary,) generally triangular, and terminating in three 
long arms, each of which ends in three minute spines. Hab. West Point. 
The number of arms is usually three, but I have met with 
specimens in which one corpuscle had three and the other four 
arms, others in which both had four, and others again in which 
both had five arms. 
It appears to me that the five-armed variety may have given 
rise to the genus Pentasterias, (page 290,) and the four-armed. 
les are possibly the same as Staurastrum, (page 289.) This 
however is only a conjecture, hazarded without having seen al 
thentic specimens or good figures of those genera. The struc 
ture of the arms is exactly as in the Xanthidium, (fig. 15, Pl- 1, 
and there is indeed an evident relation between the genera. 
