>9°5-l 



ORTMANN — AFFINITIES OF CAMBARUS. Ill 



This section is formed to receive an isolated species, the position 

 of which seems quite uncertain. There is a remote resemblance of 

 the sexual organs to those of C. difficilis of the third section of this 

 subgenus, and in other characters there are resemblances to C. mis- 

 sissippiensis, namely in the lack of marginal spines of the rostrum, 

 and in the obliteration of the areola. The annulus of the female 

 agrees with C. palmeri in being depressed in front, and prominent 

 and tuberculated behind : but a similar shape is found in the sub- 

 genus Bartonius. On the other hand, also the male sexual organs 

 can be compared with Bartonius, although they are by no means 

 identical with the very uniform type seen in the latter subgenus. 

 The chelae, according to the description, are very peculiar, namely 

 long and subcylindrical, the palm with subparallel margins : this is 

 entirely unlike anything that is seen in the virilis-section of the 

 present subgenus, and rather stamps this species a primitive one. 

 Then, again, this species presents in the elongate rostrum and 

 antennal scale very unusual features. 



Thus it is hard to form a positive opinion about its position. I 

 should not hesitate to place it with the palmeri-group of the virilis- 

 section, if it was not for the primitive character of the chelae. Ac- 

 cording to the latter, and possibly also according to the sexual 

 organs, we might place it at the beginning of the subgenus, as a 

 peculiarly developed primitive form, but It also may be the most 

 highly specialized form of the subgenus. The distribution (Mis- 

 sissippi and northeastern Arkansas) would fit either assumption. 



KEY TO THE SPECIES OF THE SUBGENUS FAXONIUS. 



i. Section of C. limosus (see p. 108). 



«j Generally third and fourth pereiopods with hooks in the male. Carapace sub- 

 cylindrical. Areola wide and long. Chela; subcylindrical. Eyes rudi- 

 mentary. C. (Faxonhts) pellucidvs (Tellk. ). 

 rtj Only third pereiopods with hooks in the male. Carapace ovate, depressed. 

 Areola rather wide, of medium length (about half as long as anterior 

 section of carapace). Chelae not subcylindrical, compressed, and more 

 or less ovate. Eyes well developed. 

 b x Sexual organs thick, swollen in the middle, tips short and stout, both 

 slightly curved in the same direction. C. (Faxonius) harrisoni Fax. 

 b 2 Sexual organs short, thick, but not swollen, straight. Tips divergent. 

 i\ Sides of carapace with one spine behind the cervical groove. 



d x Sexual organs with tips not crossed, the outer directed outward, 

 the inner inward. C. (Faxonzus) sloanei Bund. 



