THE LOESS OF NATCHEZ, MISS. 315 



maxillatum, which is the common form in the south. Poly- 

 gyra monodon is the form usually named /eai\ and P. monodon 

 fraterna is the form generally known as typical monodon.* 



The modern shells and the two fossils are of the leai type, 

 but have a smaller umbilicus than the northern form. Most 

 of the fossils are of the larger fraterna type. It was at first 

 thought by the writer that the fossil shells of Gastrodonta 

 multidentata might be G. lamelhdens Pilsbryf, but a careful 

 examination of the teeth shows that the fossils are without 

 doubt G. multidentata. Modern G. multidentata is reported 

 from southeastern Tennessee by Ferris. J 



Fossil Pyramidula alternata and var. costata are not always 

 sharply distinguishable, but the specimens listed as costata all 

 show more or less clearly the coarse ribs which characterize 

 this southern variety. 



Succ inea ovalis Say is the species well known as S.obliqua. § 

 The snails' eggs could not be identified, but they are undoubt- 

 edly eggs of land snails. Two species were collected. 



The Natchez loess is of special interest because it furnishes 

 particularly weighty arguments against both the aqueous and 

 glacial theories of the origin of the loess. That this loess is 

 not of aqueous origin is shown by its fossils, which are terres- 

 trial upland species, and by its distribution over a high ridge, 

 higher than the surrounding country for many miles around. 

 A body of water sufficient to cover this ridge would form an 

 inland sea, with land on which the molluscs might develop 

 so remote from present Natchez hill that it would have been 

 necessary to transport them a great distance by water. That 

 it is extremely improbable that the shells of the loess at any 

 point have been transported any considerable distance by water 



*On authority of Pilsbry. — Proc. Acad. Nat. Sci. Phil, for 1900, pp. 

 454-5. 



tSee Nautilus, vol. XI, p. 134. 



X Nautilus, vol. XIV, p. 58. — 1900. 



§See The Mollusca of Chicago Area, Frank C. Baker, in Bull. Chicago 

 Acad. Sci., No. Ill, pt. 2. 



