106 ORTMANN — AFFINITIES OF CAMBARUS. [A P riii 3 , 



The more advanced forms of the subgenus Cambarus generally 

 seem to prefer the ponds, lakes, and sluggish streams of the lowlands. 

 Subgenus: Cambarellus (Type: C. montezuma). 



This subgenus corresponds to the fifth group of Faxon. 



Faxon compares the male sexual organs with those of his fourth 

 group (= Faxonius), but I rather think that they are more closely 

 allied to those of his first and second group (= subgenus Cambarus^. 

 This latter relation, with the more primitive forms of the subgenus 

 Cambarus, is confirmed by other characters : carapace and areola 

 which are rather primitive, at least not very highly advanced ; the 

 rostrum has lateral teeth, which show a tendency to disappear ; the 

 chelae are very simple, more or less elongated and subcylindrical, 

 which is distinctly a primitive feature. The annulus ventralis of 

 the female seems to be very remarkable in C. montezuma (movable, 

 fixed only at the posterior end), and also in C. shufeldti (a trans- 

 verse curved ridge, the hind side of the ridge concave). 



The three species of the subgenus may be distinguished as follows : 



a x Sexual organs of male with straight terminal teeth. Carapace with lateral 

 spines. Rostrum with distinct marginal spines. 



C. {Cambarellus) shufeldti Fax. 

 a 2 Sexual organs of male with curved terminal teeth. Carapace without lateral 

 spines. Rostrum with or without marginal spines. 



6 1 Carapace slender and subcylindrical. Rostrum longer and narrower, 

 with sharp marginal spines, and long, spiniform acumen. 



C. {Cambarellus) chapalanus Fax. 

 /'., Carapace ovate. Rostrum shorter and wider, with or without marginal 

 spines, in the first case, the acumen is much shorter. 



C. [Cambarellus) montezuma Sauss. 



C. shufeldti is apparently more primitive than the other two 

 species. I have no doubt that Cambarellus took its origin from the 

 most primitive species of the subgenus Cambarus (digueti-group) , 

 but developed in a peculiar direction, which is chiefly characterized 

 by the male sexual organs, and by the presence of hooks on the 

 second pereiopods, a condition that is found nowhere else in the 

 genus. 



The distribution of this subgenus also suggests its antiquity, for it 

 is characterized by a strong discontinuity, C. shufeldti being found 

 in Louisiana, the other two species in Mexico. This geographical 

 discontinuity is accompanied by morphological discontinuity, the 

 former species differing very strongly from the two latter. While 



