106 ORTMANN— AFFINITIES OF CAMBARUS. fAprii 13, 
The more advanced forms of the subgenus Caméarus generally 
seem to prefer the ponds, lakes, and sluggish streams of the lowlands. 
Subgenus: CAMBARELLUS (Type: C. montezsume). 
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 Caméarus). 
This latter relation, with the more primitive forms of the subgenus 
Camébarus, 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 
chelze 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. montezume (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, Sexual organs of male with straight terminal teeth. Carapace with lateral 
spines. Rostrum with distinct marginal spines. 
C. (Cambarellus) shufeldti Fax. 
a, Sexual organs of male with curved terminal teeth. Carapace without lateral 
spines. Rostrum with or without marginal spines. 
6, Carapace slender and subcylindrical. Rostrum longer and narrower, 
with sharp marginal spines, and long, spiniform acumen. 
C. (Cambarellus) chapalanus Fax. 
6, Carapace ovate. Rostrum shorter and wider, with or without marginal 
spines, in the first case, the acumen is much shorter. 
C. (Cambarellus) montezume@ Sauss. 
C. shufeldti is apparently more primitive than the other two 
species. I have no doubt that Cambarel/us 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. shufe/di 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 
