CAMBARUS. ae 
the male. Ifthe reader is unable to determine the group to which the speci- 
mens in his hands belong, through the lack of males, the fault lies, as Dr. 
Hagen observes, not in the principle of classification, but in the scantiness of 
his material. A species involves two sexes; and until the species is known, it 
avails little to attempt the determination of a specimen in this difficult genus. 
In accordance with the above principle of division, the genus Cambarus 
falls into five subordinate groups, viz. : — 
I. Third segment of third and fourth pairs of legs of male hooked. First 
pair of abdominal appendages of male with outer part truncate at the tip, 
with one to three recurved teeth; inner part terminated by a short acute 
spine, which is generally directed outwards. Type, C. Blandingii. 
II. Third segment of third pair of legs of male hooked. First pair of 
abdominal appendages of male as in Group I. Type, C. advena. 
HII. Third segment of third pair of legs of male hooked. First pair of 
abdominal appendages of the male thick, terminated by two recurved teeth, 
the larger of which is formed by the tip of the outer part of the appendage, 
the smaller by the inner part. Type, C. Bartonit. 
IV. Third segment of third pair of legs of male hooked. First abdomi- 
nal appendages of male terminating in two elongated, nearly straight, acute 
tips. Type, C. affinis. 
V. Third segment of second and third pairs of legs of male hooked. 
Type, C. Montezume. 
GROUP I. (Tyre, C. Blandingii.) 
Third segment of third and fourth pairs of legs of male hooked. First pair of 
abdominal appendages of male with outer part truncate at the tip, and furnished 
with one to three small recurved teeth ; inner part terminated by a short acute spine, 
which ts generally directed outwards. 
In this group the rostrum is generally triangular, with a small tooth on 
each side, near the apex ; in C. Leconte’, C. spiculifer, C. versutus, and C. pubes- 
cens, the lateral teeth are more strongly developed. The chelx are slender 
and covered with flattened, squamous tubercles, ciliated in front. The male 
appendages are tipped with two or three small curved teeth (corneous in the 
first form), and armed on the inside with a sharp spine directed obliquely or 
horizontally outwards. The terminal teeth are very minute in C. fallax. 
3 
