628 NORTH AMERICAN ASTACID.E FAXON. 



Ill connection with Miss Hoppin's observations on the crepuscular 

 habits of this species it is interesting to note that the atrophy of the 

 visual organs has not progressed so far as in the other blind crayfishes 

 of the United State?, C. pellucidus and C. hamulatus.* In other respects, 

 also, C. setosus is more closely related to outside, eyed species than 

 is either of the other cave species. This doubtless results either from 

 the twilight conditions under which it lives, or more probably from its 

 having been subjected for a shorter period of time to cavern influences. 



The three blind species, although belonging to two sections of the 

 genus, resemble each other in the slenderness of the body and claws 

 and in the width of theantennal scale. The slenderness of the body and 

 claws in these species may be attributed to their life in caves, where 

 competition is largely removed and physical power ceases to be an im- 

 portant factor in their existence. The width of the antennal scale is 

 probably a variation correlated to the atrophy of the adjacent eye and 

 ocular peduncle. In short, these points of resemblance between the 

 three cave species, like the rudimentary state of the eye and the trans- 

 parency of the shell, are of little value from a taxonomic point of view, 

 not indicating close genetic affinity, but surely appearing in widely 

 diverse species, provided they be subjected to the same subterranean 

 life. The closer superficial likeness between C. pellucidus and C. hamu- 

 latus, belonging to different sections of the genus, than between C. ham- 

 ulatus and C. setosus belonging to the same section, may be explained 

 by the longer period of time during which the subterranean influences 

 have probably been exerted upon the first two species. 



G. C. Broadhead (Eeport of the Geological Survey of the State of 

 Missouri, 1874, p. 36) states that blind crayfishes are found in the cave 

 region of Christian County, near Ozark, in southern Missouri. It is 

 probable, from the locality, that they are the same species as those 

 from Jasper County. 



Cambarus affinis (Say). 



Additional localities: Shenandoah River, Waynesborough, Virginia 5 

 Blackwater River, Zuui, Virginia; Patoka River, Patoka, Indiana. 

 D. S. Jordan (U. S. F. C). 



The specimens from Patoka, Indiana (six males, form I; four females), 

 differ from the typical G. affinis as follows : The areola is broader in the 

 middle, there is but one lateral thoracic spine, the hepatic area is 

 smoother (merely granulate, instead of spinous), the branchiostegian 



*On the contrary, Mr. G. H. Parker concludes that the histology of the retina 

 shows more degeneration in C. setosus than in C. pellucidus. His researches on the 

 subject will shortly be published in the Bulletin of the Museum of Comparative 

 Zoology. From the external morphology alone, one would surely be justified in 

 deeming C. setosus the least modified of the three blind species. The eye-stalk and 

 external part of the eye are largest in C. setosus, smallest in C. pellucidus. C. hamu- 

 latus stands between the other two in this regard. For the aberrant position of C. 

 pellucidus in other respects, see my Revision of the Astacida), page 18. 



