Sketch of the Infusoria of the family Bacillaria, 289 
by several writers* to a “curious pinnatifid appearance” which 
this species presents “ before the ultimate separation of the joints.” 
I have not seen the filaments in this state, nor have I met with 
any detailed account of this change in the few works which I 
have been able to consult. : 
This species is extensively diffused in Europe, and. appears to 
be equally so.in this country. I have met with it from Rhode 
Island to Ouisconsin, and south to Virginia; it occurs at West 
Point in great abundance in ditches and peat bogs, where I have 
found it most abundant in early spring. I believe Desmidium 
cylindricum of Greville to be merely a state of this species. 
2. Desmidium heeaceros, Ehr. (Compare figs. 2 and 3, Pl.1.) Cor- 
puscles binary, trilateral, the points drawn out to three -horns and trun- 
cate at the extremity, ;5 of line. 
3. Desmidium aculeatum, Ehr. (Compare figs. 4, 5, and 6, Pl. 1.) 
Corpuscles spiny trilateral, the points drawn out to three truncate horns, 
often terminating in three spines, = 
I copy Ehrenberg’s description of the two last species, that 
they may be compared with the figures referred to above, which 
represent various binary triangular bodies, some of which agree 
pretty well with the above characters. ‘They however are so 
unlike D. Schwartzii, and present so many points of resemblance 
to Euastrum that I shall describe them as species of that genus, 
i STAURASTRUM. mi 
Free, a simple univalve quadrangular carapace. 
1. Staurastrum paradorum. Corpuscles rough, single or binary, 
four setaceous horns in form of a cross. 
_ Micrasterias Staurastrum, Micrasterias tetracera, didicera, tricera. 
Kutzing, Linnea, Vol. viii, p. 599, PL. 20, figs. 83, 84! and 85. 
St. paradoxum, Meyen, Nov. Act. Nat. Cur., xiv, p. 777, Pl. 43. 
‘Formed principally of two cells united end to end, and each ter- 
Minated by cross-shaped prolongations, on which are perceived vestiges 
of articulation.” See Ferussac’s Bulletin, June, 1830. | 
_ Tam not sure that I have yet met with this species in America; 
Thave, however, often seen the binary bodies represented by figs. 
3 and 4, Pl. 1, having four arms instead of the three represented 
in our drawing. In the four-armed state they agree closely with 
‘Ne above characters of S. paradorum, as well as with Kutzing’s 
"See Agardh. Systema Algarum, p. 15,and Greville in British Flora, Vol. v, p. 402. 
