466 Illinois State Laloratory of Natural History. 



Seen from the side, the shell is broadly subovate, hio-h- 

 est in the middle, but of about the same width for two 

 thirds its length; dorsal margin strongly arched, the 

 eye-spot anterior to the highest point. 



Seen from above, the shell is a narrow, much com- 

 pressed ellipse. 



Terminal segment of second foot a fourth as long as 

 the preceding segment. The two short terminal setae 

 are of the same length as the segment, the louger one 

 as long as the last three segments. 



Caudal rami short, stout, and much curved. Terminal 

 claw smooth, curved, and about half the length of ramus; 

 subterminal claw five sixths the length of the terminal 

 one, smooth, curved, twice the length of the terminal 

 seta; dorsal seta somewhat longer than the terminal 

 seta and situated slightly beyond the middle of the 

 ramus. 



This species may at once be recognized by the mesh- 

 work of anastomosing parallel longitudinal lines over the 

 entire surface of the shell (Fig. 4). These may com- 

 monly be quite readily seen, thus settling its identity at 

 once, as I am not aware of any other ostracode with 

 shell markings of this character. 



This species is quite common in most running streams, 

 and was one of the commonest forms seen in my ex- 

 amination of the collections of the Illinois State Labora- 

 tory of Natural History from various localities, and 

 of the Illinois Biological Station at Havana, 111. 



Cypria ophthalmica Jurine. (PI. XLVIL, P'ig. 5.) 



1820. Monoculus ophthalmicus, Jurine (36, p. 178, PI. XIX., Fig. 



16, 17). 

 1835. Cypris cojnpressa, Baird(l, p. 100, PL III., Fig. 16). 



1837. Cypris tenera, Koch (38. H. XII., p. 3, Fig. 3). 



1838. Cypns punctata, Koch (38, H. XXI., p. 23, Fig. 23). 



1850. Cypris compressa, Baird (2, p. 154, Taf. XIX., Fig. 14, 14a-c). 



1851. Cypris elegantula, S. Fischer (23, p. 161, PI. X., Fig. 12-14). 



1853. Cypris compressa, Lilljehorg (39, p. 112, Tab. X.. Fig. 16-18). 



1854. Cypria punctata, Zenker (75, p. 77, Taf. III., Fig. A). 



