NO i'292. CRUSTACEAXSOFNirKAJACKCAVE—HAY. 421 



uinvillino-ly, more out of (loforenco to coinnion usage than out of con- 

 tidence in the validity of the ocmius. The ease has been several times 

 reviewed by various writers, i)ut in view of the fact that in this paper 

 several new facts regarding- the species are brought forward 1 feel 

 warranted in presenting a complete digest of all that has been said and 

 adding thereto such remarks as my experience dictates. 



The genus 0^c/'<I»fra was erected in 1871 by Dr. Packard for the 

 reception of the peculiar eyeless Isopod from the cave region of Ken- 

 tucky. The original diagnosis was based on imperfect specimens 

 which lacked the uropods and second antenna?, and the name Cs&cidotea 

 was intended to call attention to its affinity to the marine genus Idotea. 

 However, a careful comparison of the structural details with this 

 genus and with AseJhm coimrmnU showed that these first ideas Vv^erc 

 erroneous and that the affinity lay with Asellus rather than Idotea. As 

 the genus Asellns is a characteristic fresh-Avater form distributed, in 

 North America, very generally throughout the fresh-water surface 

 streams and ponds of the cave region, the probable very close relation- 

 ship of the two o-enera Caecidotea and Asellus and the probable 

 descent of the blind form from the other became apparent. In 1876 

 Dr. S. A. Forbes^ united it with Asellus, and in describing his investi- 

 gations said ''A detailed comparison of this species with undoubted 

 Asellus^ espec-ialh" with the admirable plates of ^4. aquaticns in the 

 ' Crustaces d'eau douce de Norvege,' has failed to reveal any structural 

 peculiarities which could positively serve as the characters of a distinct 

 genus." In 1881 Dr. Packard described a second species of this genus 

 from Nickajack Cave, near Chattanooga, Tennessee, calling it Csecldotea 

 itickajachmsis. At the same time he stated his opinion that the two 

 species of Cceeldotea had sprung from two distinct species of AKellus. 

 Y'we years later the same author, in his monograph of the Cave Fauna 

 of North America,^ defends his genus,- and this defense has apparentlv 

 been sufficient to cause all subsequent writers to accept it. He says: 



It remains to be seen, however, wliether ]Mr. Forl)es has not somewhat overstated 

 tlie ease and whether there are not a nnniber of structural peculiarities whicli forbid 

 our placing the two known species in the genus Asellus. It should be observed that 

 not only are Cxcidotea dygla and Ciccidotca nickajaekensis without eyes, but that the 

 body and appendages also differ a good deal from any of the known species of Asellus. 

 The genus seems as well founded as many others in the Isopods and other groups of 

 Crustacea. We have little doubt but that Ciccidotea has by modification and heredity 

 been derived from Asellus, but because this is most probable it is no reason why, from 

 a systematic point of view, we should disregard its evident generic characters; for it 

 is now generally believed that somehow all the genera of Isopoda have descended 

 from some jjrimitive form or genus. Because, then, we do not know with some 

 degree of certainty that Qeddutea has recently diverged from .isellm, and can see 

 that the generic characters it possesses have been the result of its underground life, 

 we should yet, from a purely taxonomical point of view, regard it as a good genus. 

 Of the genus Crangonyx some species are blind and others are not, but the blind spe- 

 cies do not present other important differences. It is so with the species of Phalan- 



iBuli. Illinois Mus. Nat. Hist., I, 1876, p. 11. ^Mem. Nat. Acad. Sci., IV., p. 30. 



