2908: ORTMANN — AFFINITIES OF CAMBARUS. 93 
specialized types (C. graciZis and allies), and even some of the 
primitive forms (C. cudensts) possess some peculiar and apparently 
advanced characters. I think we can express it this way: among 
the second group, there are species that approach most closely the 
original stock of the genus, but they themselves are modified to a 
degree. If I am to single out a species that possibly is she most 
primitive, I should name C. adguetz Bouvier (Bull. Mus. Parts, 
1897, p. 224), which is identical with C. carinatus Faxon (Pr. 
U. S. Mus., 20, 1898, p. 648). It is remarkable that the most 
primitive forms are found in Mexico (and Cuba), which agrees 
well with the theory of the origin of the genus in these parts (see 
Ortmann, 7. ¢., 1902, p. 283). 
CHARACTERS OF THE GENUS CAMBARUS THAT SERVE TO 
DISTINGUISH GROUPS AND SPECIES. 
Sexual Organs. — Already the earlier writers (Girard, Hagen) 
have pointed out the importance of the anterior pair of abdominal 
appendages of the male (copulatory organs) for systematic pur- 
poses. Faxon made large use of them in defining his five groups, 
but within the groups he rarely tried to avail himself of these limbs 
to reveal the mutual affinities of the different species. It is now 
generally known that these organs furnish not only the best specific 
characters, but that their similarity in certain assemblages of species 
clearly indicates genetic relationship. In close connection with 
the shape of this organ is that of the female ‘‘ annulus ventralis,’’ 
as we now know, the receptaculum seminis. ‘There is, however, 
not so much variety in the shape of the latter organ, it is not so 
polymorphous, and the main types occur in different groups, which 
is apparently due to the more simple structure of this organ. 
Nevertheless, the annulus — in connection with the male organ — 
is rather important. We may add that in a number of species 
the annulus is not very well known. 
As regards the male organs, their shape is very complex and 
much varied. Several main types may be distinguished, and these 
again show much diversity. It is hardly likely that in so complex 
an organ the identical form has developed several times, that is to 
say that there are cases of parallelism ; where there is identity or 
similarity of these organs in different species, this is generally and 
surely a sign of close affinity. Only one or two exceptions in the 
