112 KANSAS UNIVERSITY SCIENCE BULLETIN. 



were also examined for shells. At Long Island, along the creek 

 bank, is an especially good exposure of Pleistocene. The Mio- 

 cene of the locality is famous for its vertebrates. 



As three faunas are represented in the one locality, it is well 

 to consider them separately. 



RECENT MOLLUSKS OF THE REGION. 



The living mollusks of the locality belong to that fauna des- 

 ignated by the U. S. Biological Survey* as Upper Sonoran. 

 As to shells, this fauna is characterized not so much by the de- 

 velopment of peculiar species or subspecies as by the absence 

 of a very large proportion of species belonging to the Carolin- 

 ian zone to the eastward. West of the Mississippi river these 

 species gradually fade out, some species and groups not ex- 

 tending as far as others. If the westward limit of the most 

 characteristic of Carolinian shells, the large toothless Poly- 

 gyras, be used for the boundary between the Carolinian and 

 Upper Sonoran zones, we find the Carolinian extending only 

 as far west as the vicinity of Topeka, Kan. This is somewhat 

 to the eastward of the boundaiy as plotted on the faunal map. 



Phillips county, lying far west of this, is wholly beyond the 

 influence of the Carolinian zone, and its fauna is typically Up- 

 per Sonoran. This zone and fauna extends northward almost 

 to the northern boundary of the United States, beyond which 

 lies the transition I'ealm; between these two there is little in- 

 termingling, the latter being characterized by a large number 

 of specialized species. 



Mollusks are not abundant in the Upper Sonoran, and belong 

 chiefly to the groups of small species; the Succineas are the 

 largest of the region. Each group, as a rule, has a different 

 habitat, but a favorable locality for many species is along the 

 base of the crumbling Miocene ledges at the tops of the hills. 

 Trees and shade are confined to the very banks of the creeks, 

 but many shells can be found on the bare prairies about the 

 bases of grasses, brush and cactus, where this is present. 



The streams are almost destitute of shells. This is doubtless 

 due to their sandy character and the fact that they go dry in 

 some seasons. Occasional deep holes in Prairie Dog creek are, 

 however, favorable for bivalves, and four species were col- 

 lected. 



* U. S. Biological Survey, Fonrth ProviBion&l Zon« Map of North Ajnerica; Merrian. 

 Bailey, NeUon, Preble, 1910. 



