292 The American Geologist. November, i903 
gidaris (Say) Try., and Snccinea grosvcitorii Lea. The first 
three species are restricted to the southern states. Snccinea 
grosvcnorii is now locally very common northward to South 
Dakota, especially in the country bordering the Missouri. Its 
center of distribution is far north of Natchez, and its south- 
ern extension may be of comparatively recent date. The spec- 
ies is very common in the northern loess along the Missouri 
river. 
The Natchez fossils bear out the writer's oft-repeated state- 
ment that the loess fossils of any given region are practically 
identical with the modern molluscan fauna of the same region.* 
Indeed, they furnish the most convincing proof of this in- 
teresting and important fact which has yet been presented. 
The most characteristic and widely distributed species of the 
northern loess, such as Hclicina occnlta, Snccinea grosvcnorii, 
Pyramidnla striatcUa, VaUonia gracilicosta, Polygyra nuihi- 
lincata znd Pnpa ninscorum, are wholly absent from the south- 
ern loess, as, with the exception of 6". grosvcnorii, they are 
from the modern fauna of that region, while Snccinea avara, 
so common in the north, and so frequent there as a fossil, is 
very rare in both the fossil and modern faunas of Natchez. 
]\Iore than one-half the species in the Natchez list of fos- 
sils have also been found in the northern loess, while the fol- 
lowing eighteen species are thus far known only from the 
loess of the south : 
Helicina orbiculata Omplialina kopnodes 
Polygyra fraudulcnfa Vitrea placeniula 
iiiflecta. Gastrodonta ligera 
" albolabris " miiltidciitata 
" cxnlcta Pyraniidula altcniata costata 
" palliata Punctum pygr.iacum 
" obstricta Sirobilops labyriufliica (probably) j- 
" clevata 
" thyroidcs bucculcnta 
" stenotrcma 
Polygyra albolabris and Piinctuni pygniaciini are the only 
species in this list which, judging from pre sent distribution, 
♦Bull Nat. Hist. St. Univ. Iowa, vol. I. p. 213.— 1S90. 
Proc la. Acad. Sci., vol. Ill, p. 84.— 1S9G. 
Proc' la. Acad. Sci., vol. V. p. 41.— 189S. 
Proc' la Acad. Sci.. vol. VI. p.99.— 1S99. 
Jour." Geol., vol. VII. p. 132.-1899. 
+The S. labrrinthica of the earlier reports on northern loess fossils is 
probably all S. virs-o. 
