312 NATURAL HISTORY BULLETIN. 



The number of modern shells of each species found at Nat- 

 chez is given in the last two columns of the table. In order 

 that some conception of the peculiarity of the local distribu- 

 tion of modern shells may be gained, the collections made on 

 the bluffs toward the north are listed separately from those 

 which were taken on the hills southwest of Natchez. The 

 grouping of the fossils of the species in the loess is singularly 

 like that of modern shells on the surface. 



The modern shells were all collected on higher slopes. No 

 collections were made on the Mississippi bottom lands. 



Polygyra claiisa should be added to the list of Natchez fos- 

 sils on the authority of Binney. 



It will be noticed that all the species of the accompanying 

 table are terrestrial, and all are now found living either on the 

 hills in the immediate vicinity, or in similar situations in other 

 parts of the south. The fossil molluscan fauna of Natchez 

 resembles the modern fauna of the southern spurs of the Cum- 

 berland mountains in northern Alabama and Georgia, so far as 

 terrestrial forms are concerned only, for it contains no aquatic 

 species. It therefore presents a distinctly southern facies. It 

 belongs to the fauna of the interior region of the eastern pro- 

 vince of Binney,* and with the possible exception of Vertigo 

 tridentata and Sphyradium edentulum, all its species are now 

 found living in the southern part of that region, within the 

 limits of which Natchez is located. The distribution of Ver- 

 tigo tridentata has not yet been satisfactorily determined, 

 partly because the species is often overlooked on account of 

 its small size, and partly because it has commonly been con- 

 fused with other species. It has, however, not yet been re- 

 ported south of the Ohio river. SpJiyradiiim edentulum, which 

 now seems to be restricted to the northern region, is a com- 

 mon fossil in the loess of the upper Mississippi drainage, and 

 was evidently once much more widely distributed. It is also 

 a species rather easily overlooked on account of its small size, 

 though it is more readily recognized than the preceding 

 species. 



*Terr. Air- Br. Moll., vol. V, pp. 26-34. 



