CAMBAEUS. 17 



the male. If the 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, G. Blandmgii. 



II. Third segment of third pair of legs of male hooked. First pair of 

 abdominal appendages of male as in Group I. Type, C. ddvena. 



III. 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. Bartonii. 



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. Montezuma: 



GROUP I. (Type, C. Blandingii.) 



Third segment of I hint and fourth pairs if legs if male hooked. First pair of 

 abdominal appendages if mule ivith outer part truncate of the tip, and furnished 

 ivith "in' In three small recurved teeth ; inner part terminated by a short acute spine, 

 which is generally directed outwards. 



In this group the rostrum is generally triangular, with a. small tooth on 

 each side, near the apex; in C. Lecontei, G. spieulifer, C versutus, and ('. pubes- 

 cens, the lateral teeth are more strongly developed. The chela 1 are slender 

 ami 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 



