INFUSORIA. 59 
lobed than Fig. 27, is probably only an older state of the same. They occur at West- 
Point ; also near Detroit, Michigan, and in Ouisconsin. 
Euasfmm -. (Fig. 28, a, b.) This species is neither lobed nor undulate; but while the general 
outline is convex, a minutely serrated edge may be seen. When thro^vn on its side, (Fig. 27, b,) 
it presents an unusual thickness. 
If this species is compared with Fig. 38, PL 21, the close relation existing between the 
genera Closterium and Euastrum will be manifest. 
Euastrum -. (Fig. 29, PI. 21.) I suspect that the bodies represented in Fig. 29, belong to this 
genus. They consist usually of four somewhat elliptical green bodies placed parallel to each other, 
and united laterally, as seen in the figure. Each elliptical portion is bidentate at the ends. I have 
met with specimens in which eight such corpuscles were united, producing such an appearance as 
would be given if a figure like that shown in Fig. 29, had a similar one added immediately below it. 
If this is a species of Euastrum, perhaps it may be thus characterized: Euastrum-. 
Binary (or sometimes quaternary); each corpuscle divided by deep lateral sinuses into two 
transverse somewhat elliptical bidentate portions, the middle portions longest. Occurs in 
ponds near West-Point. 
Euastrum margaritiferum, Ehr. (Fig. 8, a, b, PI. 1.) Body binary, elliptical, each part semi-orbi¬ 
cular with the margin entire, to line. Heterocarpella tetrophthalma, Ktz. (Linn. 1833, 
PI. 19, Fig. 87.) 
Our species (Fig. 8) agrees pretty well with the above description, and with Kiitzing’s 
figure. A figure given by Meyen in his Pflanzen Physiologie, Vol. 3, PI. 10, Fig. 31, appa¬ 
rently belongs to this species also. 
The surface has a great number of minute hemispherical projections, disposed in a quin- 
cuncial order. It is possible that the 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 molecules as in Closterium, sometimes indeed the whole cavity is filled 
with such particles. Meyen states that the species he represents (1. c. Fig. 31, PI. 10) 
contains globules of starch. 
This species is very common in the neighborhood of West-Point. I once found, in the 
spring of the year, in a small pool caused by the melting of the 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. 
Euastrum -. (Fig. 9, PI. 21.) Binary, triangular, angles rounded, each corpuscle having several 
rows of minute points. Hab. West-Point. 
Euastrum -. (Fig. 10, PI. 21.) 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. 
Euastrum -. (Fig. 13, PI. 21.) Binary, corpuscles cordate at base, each having six pairs of 
short spines. 
