The Loess of Natchez, Miss. — Shiniek. 291 
hills in the immediate vicinity, or in similar situations in other 
parts of the south. The fossil molluscan fauna of Natchez re- 
sembles the modern fauna of the southern spurs of the Cum- 
berland mountains in northern Alabama and Gecjrgia, 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 
Province of Binney,* and with the possible exception of Verti- 
go tridentata and S phyradiuni cdentiiluin, all its species are 
novv found living in the southern part of that region, within 
the limits of which Natchez is located. The distribution of 
Vertigo tridentata hsis 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 confused 
with other species. It has, however, not yet been reported 
south of the Ohio river. Sphyradiwn edentiiluin, which now 
seems to be restricted to the Northern Region, is a common 
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. 
Not only do so many of these species occur in the south- 
ern part of the Interior Region, but several are restricted to it. 
Such are Helicina orhicnlata, Polygyra stenotreuia, Polygyra 
thyroides bucculcnta, Oinphalina kopnodes, Vitrea placentnla 
and Pyrauiidula alteniata costata. Polygyra obstricta and P. 
inflect a, whose northern range is but little greater, may alsa 
be added to this list. The predominance of the larger species 
of land shellsf is also characteristically southern, the Natchez, 
fauna approaching that of the Cumberland sub-region. More- 
over, the small form of Polygyra hirsnta, the Polygyra mono- 
don with nearly closed umbilicus, and the large form of Cir- 
cinaria concava, all suggest a southern origin, the fossils being 
like the predominating corresponding living forms in that 
section. 
Only four species of modern molluscs occurring at Nat- 
chez were not found as fossils. They are: Polygyra espiloca 
(Bid.) Binn., Oniphalina laevigata (Pfr.) Pils., Gastrodonta 
♦Terr. Alr-Br. Moll., vol. V, pp. 2G-34. 
tSee Plate XIV, 
