NO. 1659. AMERICAN SPECIES OF SYNALPHEUS—COUTlflRE. 



41 



M. Diguet, which is absohitely typical and which it is impossible to 

 separate as a distinct ''race,'' a rare circumstance among the 

 Synalpheids. 



On the other hand, S. nohilil is very easily distinguished from S. 

 sanlucasi, in which all the appendages, namely, the antennules, the 

 spines of the basicerite and of the anterior margin, the large chela, 

 the feet of the second pair, and the feet and even the dactyls of the 

 third pair are much shorter and more massive. 



SYNALPHEUS SANLUCASI. new species. 



Species of each of the specific groups composing the genera 

 Alpheus and Synalpheus are often parallel to species of closely'^allied 



Fig. 23. — Synalpheus sanlucasi. a, frontal and antennal region ; A", large chela ; 



1, FOOT OF SECOND PAIR ; m, FOOT OF THIRD PAIR ; m', DACTYL OF THIRD PAIR. 



groups in the characters upon which the separation of specific forms 

 is based ; as, for example, in the presence or absence of the superior 

 spine of the basicerite or of the antennal scale, the slender or swollen 

 form of the carpocerite, the spinose or unarmed palm of the large 

 chela, and slenderness or stoutness of the thoracic feet. When one 

 of these characters has been recognized in the species of a given 

 group one can almost prophesy the existence of another species pro- 

 vided with the opposite character. This is, moreover, a well-known 

 fact in all genera which are rather numerous in species. 



