1896.] NATURAL SCIENCES OF PHILADELPHIA. 495 



the special localities east and west are more or less isolated. Its distri- 

 bution is, on the whole, more markedly discontinuous than that of 

 any American land snail known to me. It probably lives in higher 

 latitude than any other member of the Helicinidce. H. occulta is an 

 omnipresent, and therefore characteristic, fossil of the Mississippi 

 Valley loess ; and during the formation of that deposit was exten- 

 sively diffused and excessively numerous over a large area where it 

 is now extinct. 



T^NIOGLOSSA. 



Family AMNICOLID^ Try on. 



66. Somatogyrus aureus Tryon, 



Nolachucky River, near Greeneville (69284). 



67. Pomatiopsis lapidaria (Say). 



Banks of Emory River, near Harriman (69283). 



Family VIVIPARID^ Gill. 



68. Vivipara intertexta (Say). 

 Samburg, Reelfoot Lake (69249). 



69. Campeloma ponderosum (Say). 



Tennessee River, near Chattanooga (69232, 69236, 69237); 

 Holston River, 1 mile above French Broad (69259, 69260) ; Ten- 

 nessee River, near Knoxville (69258) ; Clinch River, below Pat- 

 ton's Ferry (69261) ; Indian shell heap, Williams Island (69231). 



70. Campeloma subsolidum (Anth.). 



Samburg, Reelfoot Lake (69233, 69234, 69235) ; Big Harpeth 

 River, near Bellevue (69263). 



71. Campeloma geniculum (Conr.). 



Emory River, near Harriman (69262). 



72. Lioplax subcarinata (Say). 



Big Harpeth River, near Bellevue (69238). 



Family PLEUROCERID^ Fischer. 



This has long been recognized as one of the most difficult families 

 of American mollusks. Tryon made a good beginning in the in- 

 tricate study of its species in his monograph published by the Smith- 

 sonian Institution in 1872. His conclusions were based upon a 

 study of material from all the principal collections of that time ; 

 and his extensive synonymy has proved in nearly every case which 



