STALK-EVED CRUSTACEA 221 



dages of first segment with extremity very large and 

 vertically compressed. 

 Guatemala. 



35. Pseudothelphusa lamellifrons. 



Resembles Pseudothelphusa bocourti, except the ab- 

 domen of the male contracts at the fifth segment, and 

 the sixth segment is longer than the seventh. The 

 extremity of the appendage of the first segment is 

 laminate, and folded and compressed laterally ; the outer 

 side has a blunt tooth pointing forward and outward, and 

 the inner side has two lobes. Teeth on lateral edge very 

 minute. 



Mexico. 



2. Potamocarcinus. 



Potamocarciniis . H. Milne Edwards. M. J. Rathbun, 



Ortmann. 

 Kingsleya . . . Ortmann. 



Resembles the genus PseudothelpJiusa. The superior 

 frontal crest is sharp and lamellate, overhanging the front, 

 which is rapidly retreating ; the orbits are very deep, the 

 margins above and below making deep semicircular 

 incisions in the carapace, and having below two angular 

 sinuses ; the antero-lateral borders have strong spines. 



Synopsis of the Species. 



A. External appendage of the external maxillipedes 

 reduced to a stump, being less than one-third the length 

 of the third joint. — {P. latifrons.) 



B. The external appendage of the external maxillipedes 

 is more than one-third the length of the third joint. 



