126 SKETCH OF THE INFUSORIA 



12. Euastrmn . (Figs. 11 and 12, PL I.) Binary, each cor- 

 puscle elliptical and terminating at each extremity in a single spine. 

 Hab. West Point. 



13. Euastrum . (Figs. 2, 3, 4, 5, 6, and 7, PI. I.) Binary, 



(sometimes quateniary,) generally triangular, and terminating in 

 three long arms, each of which ends in tliree minute spines. Hab. 

 West Point. 



The number of ai-ms is usually three, but I have met with 

 specimens in which one corpuscle had three and the other four 

 ai-ms, others in which both had four, and others again in which 

 both hadj^?;e arms. 



It appears to me that the five-armed variety may have given 

 rise to the genus Pentasterias, (page 118,) and the four-armed 

 ones are possibly the same as Staurastrum, (page 118.) This 

 however is only a conjectm-e, hazarded without having seen au- 

 thentic specimens or good figures of those genera. The struc- 

 ture of the arms is exactly as in the Xanthidium, (fig. 15, PI. I,) 

 and there is indeed an evident relation between the genera. 



The reader is requested to compare some of the figures last 

 referred to, with the descriptions of Desmidium hexaceros and D. 

 aculeatum, page 117. 



14. Euastrum . (Fig. 14, PL I.) Binary, corpuscles trian- 

 gular, each angle terminating in a sharp spine. Hab. West Point. 



I have seen several other species of Euastrum, but the number 

 figured is sufficient to give an idea of the variety and beauty of 

 the forms in this interesting genus. 



cLOSTERiuM. {See Figs. 30 to 38, PL I.) 

 Ehrenberg makes of this genus a distinct family of Ixfusoria, 

 which he calls the Closterina, and chai-acterizes thus : 



'■'■ Polygastric [distinctly or probably) ivithout alimentary ca- 

 nal, without appendices, polypidoms having the form of a ivand, 

 (^^baguette,^^) thread or spindle, by spontaneous division, papillce 

 fixed and movable in the opening of the carapace P 



I have before stated that I consider the genus Clostcrium most 

 closely related to Euastrum, and therefore witii the Dcsmidiacea 

 generally. This relation to Euastrum is manifest in their appa- 



