jgj8.1 fcENnJS DIASTYLIS. 313 



*An excellent specimen of this sliell occurs in the 

 collection of the Academy presented by Mr. O'Keily;, 

 of Dublin, Ireland, 



xin jlccount of the Crustacea of the United States. 

 By Thomas Say, Read June 10. 1818. 



(Continued) 



Genus ^MABTYIJS f 



Essential Character, 



Feet hi^di antennce destitute of accessory scales; 

 iml with a single bifid style on each side of the first 

 segment, second segment terminated by a simple one* 



JS^atural Character^ 



T7i(?raa::;six-join ted, anterior one much larger than the 

 others conj uctly, laterally deflected, compressed, embra- 

 cing the sides,and rostrated; rostrum pcrmanent,concave 

 beneath, concealing the base of the intermediate anten- 

 nae; antennce four, placed on nearly the same horizontal 

 line, inner ones four-jointed, three basal joints robust, 

 first and second subequal, very short, concealed by tlitt 

 rostrum, third joint articulated, as long as the two pre- 

 ceding ones conjunctly, bifid, inferior division much 

 ithovter, exterior antennae simple, longer than the i^tor- 



"1; In aJlUsion to the caudal appendices^ 



