ASTACIDJE. 107 



exclusion or representation of particular species. New explorations 

 would no doubt very soon and perhaps entirely alter any views we 

 might form from incomplete materials. 



C. acutus, C. virilis, C. Bartonii, and C. obesus are the most widely 

 spread species. 



The geographical distribution according to the river systems is as fol- 

 lows : — 



The rivers west of the Mississippi, running to the Gulf of Mexico, are 

 little explored. From Texas, perhaps from the branches of the Colo- 

 rado, C. Clarkii, C. virilis, and C. jplacidus are cited ; the two latter were 

 collected by Mr. Stolley, the locality not being given. 



The Mississippi and its numerous well-known affluents contain a great 

 number of species. In the lower part of this river, and in its inferior 

 affluents, especially near its mouth, as at New Orleans, occur C. acutus, 

 C. Clarkii, C. obesus ; a little higher up in the branches on either side 

 are found C. Clarkii, C. Lecontei, C. lancifer, C. obesus. 



The Ohio River and its affluents furnish C. virilis, C. placidus, C. juve- 

 nilis, C. rusticus, C. Bartonii ; while in the Wabash River, one of its lower 

 branches, occur C. acutus and C. propinquus. The fauna of the Ohio 

 River is also quite different from that of the Lower Mississippi, if we ex- 

 clude from consideration C. acutus and the two species C. virilis and 

 C. placidus, which are found in the Colorado River. 



The middle part of the Mississippi, the Missouri, with the Osage River 

 and their several branches, contain C. acutus, C. obesus, C. Nebrascensis, 

 C. placidus, C. virilis, C. juvenilis, C. Bartonii ; the three latter species 

 being from the Osage River ; also nearly the same species as are cited 

 hi the Ohio fauna. 



In the Upper Mississippi and its affluents, especially in the Illinois 

 River, are found C. acutus var. A., C. troglodytes, C. virilis, C. placidus, C. 

 propinquus, C. immunis, C. obesus. It is worthy of remark that a channel 

 unites the Illinois and the Chicago Rivers, and that perhaps in this 

 way may be explained the occurrence of the southern species C. acutus 

 and C. obesus at Evanston, on Lake Michigan. Among the several rivers 

 and their branches lying to the east of the Mississippi, it may be added 

 that the Mobile River contains C. Clarkii, C. Lecontei, C. versutus, C. 

 immunis ; while in the Florida rivers occur C. Lecontei and C. fallax. 

 Two of them, C. versutus and C. fallax, are not as yet known farther 

 to the west. 



The rivers east of the Alleghany Mountains furnish in Georgia, 0. 

 troglodytes, C. Lecontei, C. spiculifer, C. angustatus, C. maniculatus, C. penicil- 

 latus, C. extraneus, C. latimanus, G. advena, C. Carolinus ; also besides the 

 first two a quite different and new fauna. Farther north, in South 

 Carolina, live C. acutus, C. troglodytes, C. Blandingii, and C. penicillatus ; 

 in North Carolina, C. acutus, C. Lecontei, and C. immunis, — species which 



