236 ' BULLETIN OF THE 



the Upper Mississippi valley to some extent favors the idea of a deriva- 

 tion from it of C. setosus. The greater differences between C. pellucidus 

 and all the known eyed species point toward a longer subjection of that 

 form to the spelsean influences. For comparison we give diagrams of 

 details of structure, antennal lamina, epistoma, and the two forms of 

 the anterior pairs of abdominal appendages of several species. These 

 are taken from the specimens and from the drawings. . The degrees of 

 affinity are well indicated by the shapes of the first pairs of abdominal 

 legs. The slighter approach of C. pellucidus toward C. virilis is shown 

 by Figures 1 2 to 14 of the former, as compared with Figures 8 to 1 of 

 the latter ; and the nearness of C. setosus to C. Bartonii is apparent in 

 Figures 1 and 2 of the first, and 4 and 5 of the second. Figures 11 

 and 15 represent C. hamulatus, from the Tennessee caves, a form which 

 stands between C. setosus and C. pellucidus, nearer the former. Distribut- 

 ing the mentioned species into the groups arranged by Professor Hagen, 

 we shall have the aberrant form C. pellucidus in the first group, nearest 

 to the second, in which C. virilis belongs ; while C. Bartonii, C. setosus, 

 and C. hamulatus fall into the third group. Such close affinities as exist 

 between C. Bartonii and C. setosus do not permit their separation into 

 different genera, and the retention of the latter in the genus Carnbarus 

 cannot but be followed by the disestablishment of the genus Orconectes 

 and the return to the older genus of the two species heretofore included 

 in the later. Very young specimens of C. setosus correspond better with 

 the adults of C. Bartonii; their eyes are more prominent in these stages, 

 and appear to lack but the pigment ; the rostrum also is less acuminate, 

 and its blunt lateral angles are present. The gonopods of the very 

 small ones agree with those of form ii. of C. Bartonii, the adult shapes 

 approaching those of form i. According to Miss Hoppin, the young of 

 C. setosus when alive are not so white as the older ones. 



" At first, I attributed it to greater transparency, but now I am sure the 

 color is in the shell, not that the internal organs can be seen because of the 

 transparent shell. They are not so dark, however, as the brook species 

 [C. virilis] of the same size." 



In similarity to the case of Amblyopsis, the presence of the same 

 species of blind crayfish in the caves of Kentucky and those of Indiana 

 is an indication of distribution from a single point of origin. 



The Crustacea were placed in the hands of Professor W. Faxon for 

 identification. He has kindly furnished the descriptions of the new 

 species, which are given as they come from his pen. I have added on 



