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 (1. c. fig. 31, PL 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 snow in a peat meadow, a large cloud- 

 like mass in the water, which when touched, broke to pieces and 

 became diifused 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, PI. 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. 



11. 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 spine. 

 Hab. West Point. 



13. Euastrum . (Figs. 2, 3, 4, 5, 6, and 7, PL 1.) Binary, 



(sometimes quaternary,) generally triangular, and terminating in thi-ee 

 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 th)-ee and the other four 

 arms, others in which both had four, and others again in which 

 both had^ve arms. 



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

 rise to the genus Pentasterias, (page 290,) and the four-armed 

 ones are possibly the same as Staurastrum, (page 289.) This 

 however is only a conjecture, 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. 1,) 

 and there is indeed an evident relation between the genera. 



