HANNA AND JOHNSON: MOLLUSKS OF KANSAS. 115 



since the beginning of the formation of the beds, because they 

 are found from the bottom up. But in the Prairie Dog creek 

 beds there are found no less than twenty-six species which do 

 not live to-day within several hundred miles of the formation. 

 They are as follows: 



Psidium sp? Vitrea hammonis. 



Psidium sp. Pyramidula cronkhitei cockerelli. 



Sphserium sp. Punctum pygmaum. 



Ancylus parallelus? Sphyradium alticola. 



Lymnxa parva. Sphyradium hasta. 



Lyynnxa obrussa? Pupilla muscoriim. 



Lymnxa hiimilis. Bifidaria vicclungi. 



Lymnxa desidiosa. Vertigo modesta. 



Planorbis trivolvis. Vertigo gouldi. 



Planorbis tnincatus. Vertigo martini. 



Planorbis deflectus. Sticcinea avara. 



Zonitoides arborea. Succinea sillimani. 



Euconuhis fulvus. Carychium e.i-ile canadense. 



Great changes in climate must have taken place in order 

 that this number of species should completely die out of the 

 region. Many of these twenty-six species never could have 

 lived on a barren, sandy, treeless plain. The entire surround- 

 ings must have been vastly different in regard to water and 

 vegetation for the existence of such moisture-loving forms as 

 Vertigo, Carychium, Euconulus, etc. 



Of these twenty-six species fully 50 per cent are associated 

 at the present time with a cold climate. They live in Canada 

 and the northern parts of the United States and among the 

 peaks of the Rockies. The natural conclusion to be drawn 

 from this is that the Prairie Dog creek fauna lived during ? 

 cold epoch. 



It may be stated that the fauna is as different from the loess 

 fauna as from the recent fauna in the loess region. 



It is generally admitted that the loess deposits are post- 

 glacial. Their existence on the top of glacial drift indicates 

 this, as also does the presence of a uniform fauna from bottom 

 to top. If the deposits were formed during and after glacial 

 time the bottoms would contain a different fauna from the top. 

 The presence of the northern fauna in the Prairie Dog creek 

 beds is good evidence that it is older than that of the loess, 

 and that it lived during an invasion of cold from the north. 



The Glacial Epoch, during which there may have been as 

 many as five ice sheets in some localities, is the only descent 



