XANTHO RIVULO8A. 55 



being very slightly deflexed ; the front nearly straight, 

 projecting, the margin minutely beaded. The latero- 

 anterior margin with four triangular teeth, the posterior of 

 which reaches scarcely beyond the line of the posterior 

 edge of the gastric region ; the inequalities of the surface 

 and the intervening grooves, are not very strongly marked. 

 The anterior legs are large and strong, the wrist bituber- 

 culated ; the moveable finger has a distinct groove on the 

 outer side of the upper surface, extending from the joint 

 nearly to the extremity. The remaining pairs of legs are 

 compressed, and the upper edge of all the joints ciliated. 



The general colour is yellowish, with red markings ; the 

 fingers brown, sometimes but little darker than the rest of 

 the shell. The specimens which I have seen have all been 

 smaller than the full size of X. florida. 



It appears, then, that the present species differs from the 

 former in the following particulars : the carapace is much 

 more horizontal, the inequalities of the surface less con- 

 spicuous, the lateral teeth more angular, the front less de- 

 flexed, its margin short and prettily beaded, which is not 

 the case with those specimens of X. florida which I have 

 examined. But besides these comparative characters by 

 which the two species may be distinguished, when ex- 

 amined together, there are others of a positive kind by 

 which the present animal may be readily detected. The 

 moveable finger is grooved ; the whole of the joints of the 

 legs are ciliated on the upper edge, whereas in X. florida 

 this is the case only with the third joint. The colour of 

 the pincers in this species is brown, in the other it is quite 

 black. 



There can be no doubt that this is the Cancer liydrophilm 

 of Herbst. It is figured also by Savigny in the " Crustacea 

 of Egypt ;" it occurs in Risso's " Crustacea of the Neigh- 



