118 SKETCH OF THE INFUSORIA 



Corjiuscles 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, ihat they 

 may be compared with the figures refeiTed to above, which rep- 

 resent various binary triangular bodies, some of which agree 

 pretty well with the above characters. They however are so 

 unlike D. Schivartzii, and present so many points of resemblance 

 to Euash-um, that I shall describe them as species of that genus. 



STAURASTRUM. 



Free^ a simple^ univalve quadrangular carapace. 



1. Staurastrutn paradozum. Corpuscles rough, single or binary, 

 four setaceous horns in form of a cross. 



JNIicrasterias 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, PI. 43. 



" Formed principally of two cells united end to end, and each ter- 

 minated by cross-shaped prolongations, on which are perceived ves- 

 tiges of articulation." See Ferussac's Bulletin, June, 1830. 



I am not sure that I have yet met \^nth this species in America ; 

 I have, however, often seen the binary bodies represented by figs. 

 3 and 4, PI. I, having four arms instead of the three represented 

 in our drawing. In the four-armed state they agree closely with 

 the above characters of S. paradoxum, as well as with Kutzing's 

 figm'e 83. 



PENTASTERIAS. 



Fi-ee, a simple univalve pentagonal carapace. 



1. Pentasterias margaritifera, Surface granulated, rays thick and 

 obtuse. Mandl. and Ehrenberg, 1. c. PI. 8, fig. 46. 



I am unacquainted with this genus, unless it is founded on 

 five-rayed bodies resembling figure 7, which are only varieties of 

 figures 3 and 4, the number of arms being, as I have repeatedly 

 seen, liable to much variation. 



TESSARARTHRA. 



Free, a simple carapace, univalve, globular, smooth, forming 

 chains of four or more individuals by spontaneous division. 



1. Tessararthra moniliformis. Corpuscles green, two or four united 

 in a right line. M. and E. 1. c. PI. 8, fig. 47. 



I have not noticed this genus in America. 



