16 A REVISION OF THE ASTACIDA. 
It has been noted already that in the young stages of Cambarus and Asta- 
cus the first abdominal appendages are wanting, and the telson is not divided 
by a transverse suture. In these respects the young stages agree with the 
adult condition of the Parastacinz. On this account, and on account of 
the more generalized arrangement of the gills in the Parastacinz,* it would 
seem that the Potamobiine are a more specialized type than the Parastacine. 
Further, among the Potamobiine crayfishes the genus Cambarus will hold the 
highest place by reason of the complete suppression of the pleurobranchix 
and the high degree of specialization exhibited in the first abdominal appen- 
dages and hooked thoracic legs of the males and the annulus ventralis of the 
female. In the abnormal female of Oambarus Diogenes, noticed on page 13, it 
is clearly demonstrated that an organ essentially like the first abdominal 
appendage of Astacus is the first step in the transformation of the common 
type of abdominal limb into the male appendage of Cambarus. The three 
species of Cambaroides (p. 126) form a passage from Cambarus to Astacus 
proper. 
Division of the Species of Cambarus into Subordinate Groups. — Girard divided 
the Cambari into three groups, based upon the form of the rostrum and the 
anterior pair of abdominal legs in the male. Dr. Hagen also concluded that 
the genus comprehended three well-defined groups, but he based his division 
of the genus upon the number of hooked thoracic legs in the male, taken 
in connection with the shape of the rostrum (whether toothed or toothless). 
It follows that the groups of these authors do not exactly coincide; e. g. 
C. pellucidus falls into the same assemblage of species with C. affis, C. rusti- 
cus, ete., in Girard’s system, whereas by Hagen’s mode of division it is asso- 
ciated with C. Blandingii and allied species. It seems to me that we get a 
more natural grouping of the species by taking the number of hooked tho- 
racic legs in connection with the structure of the first pair of abdominal 
appendages of the male as the basis for the division of the genus, without 
reference to the form of the rostrum. Any division based wholly or im part 
upon the presence or absence of lateral rostral spines will divorce species 
which in the totality of their organization are most closely related.- If it be 
urged against this mode of division that it implies a knowledge of the pecu- 
liarities of one sex, I reply that the same objection applies to the groups of 
Girard and Hagen, which are based in part upon characters found only in 
* Tn all the Parastacine, except Astacoides Madagascariensis, there are four pleurobranchie develope 
and the whole number of gills is twenty or twenty-one. 
