32 ASTACID.E. 



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



I. The exterior jjart is nearly trmicated 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, — C. acidus and alhed 

 sjiecies. 



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, Avhich is 

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

 conical, — C Baiioni and allied species. 



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

 exirmmis, belonging to the group of C. aji)us, has the abdominal legs 

 formed as in the group of C. Baiioni; C. advena and C. Cctrolinus, 

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

 to the group of C. acutiis. 



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

 antenna} 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 flagellum of the inner antenna^ is 

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

 the tlao-ellum is shorter, and the external branch somewhat lonojer, than 

 the inner. The antennal lamina is more elongated and enlarged before 

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

 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. fcllmidus, C. Wicgnianni, C. Carolinus, C. lancifcr, etc., lack 

 the form characteristic of their group. 



Cambarus. — Corpore elongato ; pcdihiis quint is branchiis nullis ; antcnnis 

 intcrnis ffiifjcllo lonjiori ; auro annularis apicc oporto ; pcdil/us maris tcrtiis,vcl 

 tertiis ct cpiartis articuh iertio uncjuiculatis ; pedibus at)doniinidibus maris 

 hifidis ; fcmina annido ventrali conico, pcrforato, separata. 



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



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

 gular, elongated, tvith an ante-apical tooth each side, at least in the young ; first 

 pair of atxhminal legs with the exterior part truncaied at the tip niih several 

 somewhat dilated incurved corneous teeth, occasionalhj covered with a pencil of 

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

 xmrdly directed spine. 



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

 viz. C. peniciUatns, C. Wiegnianni, and esj^ecially C. pcUucidus. 



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

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



