122 SKETCH OF THE INFUSORIA 



This is a very beautiful genus, its species presenting elegant 

 star-like arrangements of green corpuscles, some of which closely 

 resemble in form the stars and badges of honor worn in Europe. 



There appears to me to be much confusion in the specific char- 

 acters, arising from the circumstance, that the number of corpus- 

 cles in the difl'ercnt rows has been made a character of specific 

 importance. From what I have seen of the species, I am satis- 

 fied that the number of corpuscles in a star is liable to great 

 variation in the same species. Perhaps the form of the corpus- 

 cles would prove a more certain character. 



1. Micrasterias Tctras. (Fig. 19, PL I.) Four corpuscles united 

 in form of star, the edge slightly notched. 



This is a very minute species, which occurs in ponds near 

 West Point. I have also noticed it in Virginia. 



2. Micrasterias Boryana. (Fig 20, PI. I.) Ten corpuscles in the 

 exterior circle, five in the interior, and one in the centre, edge acutely 

 dentate. Corpuscles one eightieth to one hundredth of a line. 



It happens accidentally that our figui*e represents an individual 

 having just the number of corpuscles above described. I am 

 satisfied, however, from frequent observation, that the same spe- 

 cies sometimes has a much greater number of corpuscles, cer- 

 tainly «»o^/<cr roz^; o/'^//eew is often developed. It then agrees 

 with M. tricyclia of Ehrenberg. It is a very beautiful object for 

 the microscope. I have found it in New York, Virginia, and in 

 Ouisconsin. 



3. Micrasterias . (Fig. 21, PL I.) Corpuscles very numerous, 



forming large imjjerforatc plates of a circular or elHptical form. Exte- 

 rior corpuscles deeply emarginate, each having two projecting points. 



This large and very beautiful species is not uncommon in 

 ponds near West Point. 



EUASTRUM. 



Free, carapace simple, iinivalve, compressed, binary, sometimes 

 quaternary, having- the form of a two-lobed disc or lamina, often 

 dentate. 



The elegant forms and emerald gi-een color of the species of 

 this genus render them exceedingly fine objects for the micro- 



