106 ASTACID^. 



Evidently the faunal area of the second group of species coincides 

 with that of the first group in the vast regions watered by the Missis- 

 sippi and its branches, without touching, except in some aberrant forms, 

 the southeastern regions. 



The third group occurs in the whole country inhabited by the two 

 others, in the Northern Lakes and their affluents, in the rivers running 

 both to the Atlantic coast and to the Mississippi; in short, equally in the 

 northern and southern, in the eastern and western parts of the United 

 States. C. Bartonii and the next allied species are to be found in Lake 

 Superior and in the St. Lawrence River, in Nebraska, Arkansas, Louisi- 

 ana, and along the Atlantic coast from Vermont to South Carolina, and 

 perhaps to Florida. 



An interesting fact in the geographical distribution of the animals is 

 the association or exclusion of certain species, also the representation 

 of given species in different localities by others that are closely allied. 



Concerning the association of particular species, I would remark that 

 the materials before me give for two localities four species. I have 

 seen from Charleston, C. acutus, C. troglodytes, C. penicillatus, and C ad- 

 vena ; from Mobile, C. acutus, C. Lecontei, C. versutus, and C. advena. 



From six localities three species are cited : from New Orleans, C. 

 acutus, C. GlarJcii, C. obesus ; Lawn Ridge, C. acutus, C. immunis, C. obesus ; 

 Beaufort, C acutus, C. Lecontei, C. immunis ; Lake Superior, C. virilis, C. 

 propinqims, C. Bartonii; Rochester, C. propinqims, C. obscurus, C robus- 

 tus ; Osage River, C. virilis, O. juvenilis, C. Bartonii. 



Two species are quoted from more localities : from St. Louis, C. acutus, 



C. obesus ; Root Pond, C. Lecontei, C. lancifcr ; Athens, Ga., C. spiculifer, 



C. kdimanus ; Quincy, 111., C. virilis, C. placidus ; Niagara, C. affinis, C. 



propinqims ; Philadelphia, C. affinis, C Bartonii; the Mammoth Cave, C. 



pelulcidus, C. Bartonii; Cincinnati, C. rusticus, C. Bartonii; Evanston, 



111., C. acutus, C. obesus. 



The list given shows no regularity, at least I am not able to find any ; 

 still, this is perhaps because of the incompleteness of the material. 

 Looking over the species that occur together, we find the most nearly 

 related living with those that are evidently different ; those of the 

 first group with others of the second, some of the second with others 

 of the third, and even all three groups in the same locality. 



No more regularity is to be found in association of the different spe- 

 cies. C. acutus lives in seven different localities together with eight 

 different species, the half belonging to the other groups. C. advena is 

 found in the same localities with five other species, none belonging to 

 its own group. C. Lecontei, 0. obesus, C. virilis, C. Bartonii live together 

 with four, C. propinqims with five different species, partly belonging to 

 different groups. 



The uncertainty already referred to prevents my dwelling upon the 



