1818.] CRUSTACEA OF THE UNITED STATES. 241 



indurated parieties and summit often projecting a little 

 above the general surface. 



A curious parasite abounds on the body of this spe» 

 cies, perfectly distinct from the genus lone of Mr. Latre- 

 ille; a description of it will be given in its proper order. 



Genus GEBIA. 



External caudal lamellce simple; tail quadrate; anten- 

 na placed on the same horizontal Ime, interior ones short, 

 with two setae and elongated peduncles, of which the 

 third joint is much longest, exterior ones destitute of the 

 accessory lamina at base; feet ten, two anterior ones mo- 

 nodactyle with a projecting angle for a finger. 



SPECIES. 



G. * affinis. Thorax glabrous^ transversely grooved 

 in the middle by an arcuated line, behind which, on each 

 side, is a minute spine, anterior part of the thorax cover- 

 ed with numerous fascicles of short, rigid hairs, arising 

 firom short tubercles, or impressed interrupted lines some- 

 what arranged in longitudinal rows, broad before and di- 

 vided into a short canaliculated rostrum, and a prominent 

 tooth each side, which is rather shorter, and separated from 

 it by a groove, which is longer than that of the rostrum, 

 and like it glabrous, rostrum and teeth hairy to their tips, 

 the latter with a short spine beneath; eyes smaller than 

 their peduncles, which are hairy above, concealed; ante- 

 rior feet largest, ciliated with long hair beneath (except- 

 ing the carpus) on the inner edge; second joint with a 

 spine beneath, third joint with four or five beneath and 

 one above near the tip; carpus suhtriangular, with three 

 very small ones above^ five or six at tip larger, and the 



