830 



CRUSTACEA. 



The species of CorophinaB have generally the fingers of the hands 

 of the first and second pairs of legs all simple ; yet, in a few species, 

 the second pair has the fingers two-jointed, the hand being formed of 

 the fourth normal joint ; and, in a few others, the legs of neither the 

 first nor second pair are prehensile. The species also differ strikingly 

 in the stylets, and are thus naturally divided into genera. 



The posterior stylets may be exceedingly short and quite simple, or 

 they may have two short branches, ending in a few short hairs or 

 setse; or they may have two branches, the outer of which is recurved 

 uncinate at apex. The stylets of the preceding pairs, as in Coro- 

 phium and Siphoncecetes, may be subcultriform, with the outer edge 

 more arcuate and set with spines, which fits them for special action 

 by their outer margin j or they have, in common style, the two sides 

 or edges essentially alike, without spines on the outer margin or no 

 more than on the inner. These characters appear to be proper dis- 

 tinctions for genera. The importance of characteristics based upon 

 these organs will be farther considered in the remarks on the Gam- 

 maridge. Their value may, however, be obvious, from the fact, that 

 two of the forms mentioned are not found in the families Gammaridge 

 or Orchestidaa : for in no other groups, except certain Corophidae is 

 the posterior pair of stylets so short as to be concealed nearly by the 

 extremity of the abdomen, nor the other stylets spinous and arcuated 

 on the outer edge for special action by this margin. 



Kroyer has stated that the hands of the second pair in the male of 

 the Pbdocerus Leachii has the finger two-jointed, as in Erichthonius, 

 and only the female has it one-jointed, corresponding with the generic 

 character* We have not been able to verify this observation. Among 

 our species of Pyetilus (which we think may still be true Erich thonii) , 

 we observed that there were females with the finger bi-articulate, and 

 thus not at all like Podocerus. The posterior stylets in Pyetilus end 

 in a single short conical branch, with a sub-reflexed apex ; which is 

 not a form occurring in Podocerus : whether this is the form in Erich- 

 thonius, is not given in the figures or descriptions published. 



* It is possible that the Podocerus Leachii (Kroyer) should form a distinct genus, 

 as the animal lived in a tube like a Cerapus. 



