igo3 ] ORTM ANN — AFFINITIES OF CAMBARUS. 113 



a 2 Margins of rostrum straight, parallel or convergent. Marginal spines and 

 acumen not bent upward. 

 b x Acumen of rostrum long, marginal spines sharp, margins parallel. Fingers 

 of chela long. C. (Faxonius) longi digitus Fax. 



b„ Acumen of rostrum short, marginal spines small or absent, margins more 

 . or less convergent, 

 fj Acumen of rostrum not considerably shorter than width of rostrum at 

 base ; marginal spines small, but present ; margins slightly 

 convergent ; upper surface slightly concave. lingers of chelre 

 not remarkably long and not emarginate at base. 

 d x Sexual organs longer, slightly curved. 



C. (Faxonius) virilis Hag. 

 d 2 Sexual organs shorter, more strongly curved. 



e 1 Immovable finger bearded at base, chela for the rest with- 

 out hairs. C. [Faxonius) uais Fax. 

 e 2 Immovable finger bearded at base, chela pilose. 



C. (Faxonius) pilosus Hay. 



if 2 Acumen of rostrum considerably shorter than width of rostrum at base ; 



marginal spines generally wanting (rarely present and small ) ; upper 



surface deeply concave ; margins strongly convergent. Movable 



finger of chela with a deep emargination at base of inner margin. 



C. (Faxoniits) immunis Hag. 



3. Group of C. palmeri (see p. no). 

 «j Rostrum with marginal spines. 



b x Sexual organs long. C. (Faxonius) palmeri Fax. 



b 2 Sexual organs remarkably short. C. (Faxouius) dijjicilis Fax. 



a 2 Rostrum without marginal spines. C. (Faxonius) mississippiensis Fax. 



4. Section of C. lane if er (see p. no). 



Rostrum very long, without marginal spines. Antennal scale very long. Areola 

 obliterated in the middle. Chelae long, subcylindrical. 



C. (Faxonius) lancifer Hag. 



GEOGRAPHICAL DISTRIBUTION OF THE SUBGENUS FAXONIUS. 



The area occupied by this subgenus is almost entirely continuous ; 

 it extends over all of the central parts of the United States, from 

 northern Texas to Lake Winnipeg in Canada, and from Kansas to 

 the Appalachian Mountains. To the south, it hardly encroaches 

 upon the domain of the subgenus Cambarus, being found only in 

 the northern parts of Alabama and Georgia. To the North, it 

 reaches the Great Lakes, and follows down the St. Lawrence valley. 

 Eastward, the Allegheny Mountains apparently form a boundary, 

 but at two places it has crossed these mountains, namely in the 

 north, where C. limosus is found in the lowlands and rivers of 



