98 ORTMANN — AFFINITIES OF CAMBARUS. [April 13, 



ending, a character that possibly points to the condition seen in 

 the genus Potamobius ; for the rest, the terminal teeth are quite 

 variable, but always very characteristic for the species. 



It is advisable to distinguish groups within this subgenus, not 

 only with reference to the sexual organs, but also with reference 

 to the hooks of the male, for the presence of one or two pairs of 

 hooks seems to constitute, as already Faxon recognized, important 

 differences, the presence of two pairs, on third and fourth pereio- 

 pods, being evidently a more advanced stage. Using in addition 

 some other differences of the areola and the chelae, we obtain the 

 following three sections. 



1. Section : C. digit eti. 



Sexual organs of male with one to two teeth at the tip of the outer 

 part. Male with hooks on third pereiopods. Areola wide or nar- 

 row, but never obliterated, about half as long as the anterior section 

 of the carapace {incl. rostrum), or shorter. Chela elongated and 

 subcylindrical. 



2. Section : C. gracilis. 



Sexual organs of male with one to tiuo teeth at the tip of the outer 

 part. Male with hooks on third pereiopods. Areola obliterated in 

 the middle, considerably longer than half of the anterior section of 

 the carapace. Chela short, broad, ovate. 

 J. Section : C. blandingi. 



Sexual organs of male with one to three teeth at the tip of the outer 

 part. Male with hooks on third and fourth pereiopods. Areola 

 wide or narrow, rarely obliterated in the middle, shorter or longer. 

 Chela generally elongated, narrow, and subcylindrical. 



The most primitive sexual organs are found in species of the first 

 section, where there is only one tooth at the end of the outer part. 

 Similar sexual organs are found in the second (C. advena) and in 

 the third section (C evermanni} : in the latter cases, however, I 

 think we have to deal with parallelism, the single tooth in both 

 cases being due possibly to reduction. Since these two species are 

 very rare and poorly known, and since C. evermanni belongs to a 

 group that offers other difficulties, further investigations are needed. 



A closer examination may reveal the fact, that the sexual organs 

 of the digueti-group are more sharply distinguished from those of 

 C. advena and evermanni. Through the courtesy of Professor E. 

 Bouvier of Paris, I have received two cotypes (male and female) 



