128 Zoology of Colorado 



Land shells are not rarely found fossil, and from the Eocene 

 of Wyoming we have some very extraordinary forms, variously 

 related to those which now inhabit the tropical regions of America. 

 No doubt these also lived in Colorado, but the available fossil 

 land snails of Colorado are of much later date, and resemble those 

 of the southeastern United States. Oligocene time is represented 

 by Omphalina oreodontis Cockerell and Henderson, a snail about 

 24 mm. in diameter, very like the living 0. laevigata of the south- 

 ern States. Its mammalian contemporaries belonged to many 

 strange genera now extinct, but the snail, though no longer living 

 in Colorado, has left descendants of the same genus, and in fact 

 closely allied in every way. This Omphalina was found at Pawnee 

 Buttes; another species occurs in the later (Miocene) shales of 

 Florissant. Also at Florissant was found the little Vitrea fagalis, 

 seven mm. across, apparently belonging to the subgenus Paravi- 

 trea, now existing in the uplands of the southeastern states. The 

 fossil of course represents an extinct species. 



Most characteristic of the genera of Colorado snails is Oreo- 

 helix of Pilsbry, the name meaning mountain snail. Here are 

 placed the comparatively large coiled snails found in all the 

 upland rocky parts of the State, often in great abundance. The 

 genus is very old, being found as low down as the Paleocene of 

 New Mexico, but in spite of this it has not greatly extended its 

 distribution. Northward it goes to Saskatchewan and Alberta, 

 southward to New Mexico and Arizona. Its present range is evi- 

 dently contracted from the maximum as there is an outlying species 

 stranded, as it were, on Catalina Island, off the coast of California, 

 and a fossil species in the Post-tertiary deposits of eastern Iowa. One 

 might suppose that a genus of such antiquity, and long residence 

 in the same region, would have reached a condition of great 

 stability, but such is not the case. The species are so variable 

 and often so closely allied that they perplex every student who 

 tries to understand them. How many species should be recog- 

 nized, becomes largely a matter of opinion, but some of them 

 present good anatomical characters. Two forms are dominant 

 in Colorado, 0. cooperi of W. G. Binney and 0. depressa, the latter 

 assumed to be a subspecies of 0. strigosa of Gould, described 

 from Oregon. The 0. cooperi is a more globose, elevated snail, 

 more profusely banded, sometimes with the bands confluent. 



