32 ASTACID.E. 



The first abdominal legs of the males show three different forms: — 



I. The exterior part is nearly truncated at the tip, with three little 

 partly dilated corneous incurved teeth; the interior part has a short 

 acute tip, for the most part outwardly directed, — 0. acutus and allied 

 sjtecies. 



II. The two parts have elongated, straight, acute tips, — C. affinis and 

 allied species. 



III. The tips of the exterior part forms a larger tooth, which is 

 strongly recurved ; the tip of the interior part is broken, short, and 

 conical, — C. Bartoni and allied species. 



I may remark that there are three exceptions to this character: C. 

 extraneus, belonging to the group of 0. affinis, lias the abdominal legs 

 formed as in the group of ('. Bartoni} V. advena and C. ('urn/inn*, 

 belonging to the group of C. Bartoni, have the abdominal legs similar 

 to the group of C. acutus. 



The other characters examined by me are not so striking. The 

 antenna 1 are more slender, as long as, or longer than, the body in the 

 group of C. acutus: ; they are thicker and mostly shorter in the others. 

 In C. acutus and the allied species the rlagellum of the inner antennae is 

 longer, while its branches are equally long. In all the other species 

 the rlagellum is shorter, and the external branch somewhat longer, than 

 the inner. The antenna! lamina is more elongated and enlarged before 

 the middle in the group of C. acutus ; shorter and enlarged near to the 

 tip in the group of C. Bartoni ; longer and enlarged in the middle in 

 the group of C. affinis. But here are to be found more numerous ex- 

 ceptions, — C. peUucidus, C. Wiegmanni, V. Carolina*, C. lancifer, etc., lack 

 the form characteristic of their group. 



Cambarus. — Corpore elongato ; pedibus quintis branchiis nuUis •. antennis 

 internis flagetto longiori ; auro annulari, apice aperto ; pedibus maris tertiis, vel 

 tertiis et quartis articuh tertio unguiculatis ; pedibus abdomiiialibus maris 

 bifidis ; femina annub nutrali cortico, perforata, separato. 



I. GROUP. (Type, C. acutus.) 



The third and the fourth pair of legs of the males hooked ; rostrum trian- 

 gular, elongated, with an ante-apical loo'h each side, at least in the young ; first 

 pair of abdominal legs with the exterior part truncated at the tip with several 

 somewhat dilated incurved corneous teeth, occasional/// covered with a pencil of 

 hairs ; the interior pari terminated in a short, acute, ami for the most part out- 

 wardly directi d spine. 



This group seems very natural, if we except some abnormal species. 

 viz. C. penicillatus, 0. Wiegmanni, and especially C. peUucidus. 



The body and the hands are more slender and elongated. The rla- 

 gellum of the inner antennae has the branches of equal length. The 



