124 ORTMANN — AFFINITIES OF CAMBARUS. [April t 3j 



Thus the burrowing species of the diogenes-section of the subgenus, 

 while conforming in part to the original habit of living in the moun- 

 tains, have in another part abandoned their original mountain home, 

 and largely spread over the plains. That this was possible is no 

 doubt due to their peculiar way of living. Aside from C. gracilis of 

 the subgenus Cambarus, which is also a burrowing form, and occu- 

 pies a certain part of the western plains, there are no other forms 

 in the central basin that have acquired this habit, and thus C. diog- 

 ^nes did not find any competition, and was able to occupy a large 

 territory. That C. diogenes is a very vigorous and flourishing form 

 is also demonstrated by the fact that it attains, chiefly on the wes- 

 tern plains, a considerable size. 



GENERAL CONSIDERATIONS AND CONCLUSIONS. 



We have divided the genus Cambarus into four subgenera : 

 Cambarus, Cambarellus, Faxonius, Bartonius. Cambarus orig- 

 inated in Mexico, and immigrated, probably at the beginning of 

 the Tertiary, into the southwestern and southern United States, 

 originally occupying only the southwestern Cretaceous plain, the 

 Ozark Mountains, and the southern extremity of the Appalachian 

 System. A side branch, Cambarellus, has also its center in Mex- 

 ico, and spread, possibly along the sea coast, to Louisiana. In the 

 central and southeastern parts of the United States three new cen- 

 ters developed. The one is a secondary center for the subgenus 

 Cambarus, and lies at the foot of the Appalachian Mountains in the 

 lowlands of Alabama and Georgia. Here the more advanced forms 

 of this subgenus took their origin, and spread all over the Atlantic 

 and Gulf coast plain, and further up the Mississippi valley. These 

 are species inhabiting chiefly ponds, lakes, and sluggish streams of 

 the lowlands. Another subgenus, Faxonius, developed in the 

 central basin of the three great rivers, spreading over almost all of 

 the Mississippi drainage, and crossing over into the Hudson Bay, 

 Great Lakes, and even into the Atlantic drainages, probably by the 

 aid of shifting divides. The species belonging to this subgenus 

 are chiefly true river species. Finally, a fourth subgenus, Barton- 

 ius, developed in the mountainous region of the southern Appalach- 

 ians, probably including also the Ozark region, and from here it 

 spread chiefly over the Appalachian chain in a northeasterly direc- 

 tion as far as New Brunswick. Most of the species belonging 



