PACKARD ON A NEW CAYE FAUNA IN UTAH. 15& 



the caves of Kentucky, none were bleached out or differed notably 

 from those found in their usual habitats, though I am told by Prof B. 

 S. Morse that adult white individuals do occur in ordinary habitats. 



None of these animals occurred out of the cave, no species of Nemas- 

 toma or Polydesmus having been met with ; but that other forms closely 

 allied to these cave species may exist in Utah is suggested by the 

 discovery in Colorado, by Mr. E. Ingersoll (while attached to the 

 United States Geological and Geographical Survey of the Territories, 

 in 1874), of a species of Scotolemon, a genus represented by cave species 

 in Indiana, Eastern Kentucky, and Virginia, and very numerously in 

 the caves of Southern Europe. The occurrence of Scotolemon robustum 

 in Colorado is an evidence that we may have had an out-of door form 

 from which the cave rnieolous species of the Mississippi Valley may 

 possibly have been derived, or at least that the cavernicolous species of 

 Scotolemon were not independent creations. 



DESCEIPTION OF THE SPECIES. 



THYSANURA. 



Tomoceriis plumhea (Linn.) var. alba. — Several specimens of a pale 

 variety of this species of " spring-tail " occurred, some of which were 

 pure white, thoroughly bleached out, while others were more or less 

 dusky. Several of the larger specimens were pale, with traces of dark 

 markings on the body ; the antennse, legs, and "spring" were white, 

 much paler than the body. In such examples, the antennte are whitish, 

 with the two basal joints tinged with brown, the flagellum white, with a 

 slight purplish tinge. Legs and spring almost pure white. Eyes black 

 and well developed. Specimens one-half or two-thirds grown are pure 

 white, except the small black eyes, which are connected by a double 

 black line; while other specimens fully grown are perfectly white. 



Similar individuals occurred in the Carter Caves of Eastern Kentucky, 

 and still others occurred which were much darker than the Utah ones, 

 forming a series connecting the extreme white variety, alba, with the 

 ordinary plumbeous form, which latter is found in the United States 

 east of the Mississippi, Greenland, and Europe. The occurrence of the 

 white variety in a cave indicates that the ordinary form is probably to 

 be met with west of the Rocky Mountain range. 



Had I not had a series from the Carter Caves connecting the white 

 variety with the ordinary out-of-door plumbeous form, I might have 

 been inclined to regard it as a new and uudescribed species, although 

 it presents no structural differences in the form or length of the append- 

 ages from the normal form. But the series affords a capital example 

 of the successive steps in the formation of a new form, whether we call 

 it a new variety or species, while the causes of the changes are sufficiently 

 apparent. Examples such as these and others I have before me to be 

 hereafter described amount almost to demonstrative evidence of the 

 truth of the doctrine of the transformation of species. 



