80 FAUNA OF MAYFIELD'S CAVE, 



however, could not carry this species in from above, but could only- 

 make possible its entrance from below. On the other hand, the cave 

 stream comes out as a spring not 20 yards from where it disappears in 

 the cave, and to escape, this amphipod would need only to follow the 

 stream, which it could easily do during the winter and spring, or after 

 a heavy rain in any season. Similar conditions seem to exist in Donne- 

 hue's Cave, as nearly as I can determine from Blatchley's account. 

 I believe that this species has entered the cave from below and by its 

 own efforts, that it has been able to maintain itself in the cave, and 

 that it remains there in response to the proper environment. Its occur- 

 rence in several Indiana caves, in all of which it is fairly abundant, is, 

 to say the least, not inimical to this view. 



Subterranean American relatives of Crangonyx gracilis are: C. vitreus 

 (Cope) , an eyeless form, recorded from Mammoth Cave, Kentucky, and 

 Saltpeter Cave and wells at Orleans, Indiana (Packard, 1873, 95) ; 

 C. packardii Smith, having small eyes, recorded from Wyandotte Cave 

 and wells at Orleans and New Albany, Indiana (Packard, 1888, 36); 

 C. tenuis Smith, an apparently eyeless form, from wells at Middletown, 

 Connecticut (Packard, 1888, 35) ; C. lucifugus 0. P. Hay, a pale, eyeless 

 form, from a well at Abingdon, Illinois (loc. cit. , 38) ; C. mucronatus 

 Forbes, a colorless, blind species, from wells and springs in central 

 Illinois (loc. cit., 37); C. flagellatiis Benedict (1895, 617) and C. bowersii 

 Ulrich (1901, 85), blind colorless species from an artesian well at San 

 Marcos, Texas; Niphargus antennatus (Packard, 1888, 36), a pale or 

 colorless form with eyes rudimentary or lacking altogether, from Nick- 

 ajack Cave, Tennessee. 



Several subterranean species belonging to the genera Gammarus, 

 Niphargus, and Crangonyx are found in Europe and some of them are 

 known from Algeria as well (Chevreux, 1901). These are all regarded 

 by Hamann (1896), perhaps wrongly, as most authorities are against 

 this view, as varieties of a single species, Niphargus piiteanus Koch, a 

 colorless, eyeless form which he says is widely distributed in caves, in 

 the depths of Alpine lakes, and in wells in England and in nearly every 

 country of the continent. 



Still other subterrean forms, Crangonyx compactus, Calliopius suh- 

 terraneus and Gammarus fragilis (Chilton, 1894, 218-244), "transpar- 

 ent" and without trace of eyes, are known from wells in New Zealand, 

 while two blind Niphargi are known from surface waters in Victoria, 

 Australia (Sayce, 1899 and 1901). 



According to W. P. Hay, C. vitreus and C. packardii are probably 

 derived from C gracilis. The form of C. gracilis found in central 

 Indiana caves is probably another species in process of formation. 

 Already it is entitled to the rank of a variety. 



