Strophomena and Other Fossils 
63 
identical form^ associated with Strophomena nutans. In fact, 
Strophomena nutans may be regarded as only a depauperate, 
gerontic form of Strophomena concordensis. The range of Stro- 
phomena nutans also is limited to the more northern exposures 
along the areas traversed by the Cincinnati geanticline, but, 
compared with Strophomena concordensis^ its range is more 
extended, reaching from Lewis county, in Kentucky, to Dear- 
born county, in Indiana. Northward, Strophomena concorden- 
sis finds a near relative in Strophomena concordensis-huronensis 
along the northern parts of Lake Huron and along the southern 
shores of Georgian Bay. Strophomena wisconsinensis , from Wis- 
consin and Illinois, probably belongs to the same group. 
The introduction of Strophomena concordensis at the close of 
the Arnheim was brief, and the accompanying species give no 
clue as to the direction from which this fauna might have come. 
In the Blanchester division, however, the related species is 
associated with Strophomena neglecta, which finds its nearest rela- 
tive in Strophomena planodorsata from the Mississippi Valley, 
ranging from southern Tennessee northward to Minnesota and 
thence westward. Moreover, the Blanchester division contains 
also Austinella scofieldi and is included between two layers con- 
taining Hebertella insculpta, two species having an equally ex- 
tended geographical range along the Mississippi Valley. 
From these data it may be concluded that all of these species 
had some common origin. During the deposition of the Blan- 
chester division of the Waynesville there apparently was a basin 
extending from Bath, Fleming, and Lewis counties, in Kentucky, 
northward and northwestward across Ohio, Indiana, and north- 
ern Illinois, so as to connect with the Mississippi basin. Appar- 
ently Strophomena concordensis represents merely one of the first 
incursions of the fauna which later had a much greater distri- 
bution. As far as its appearance in southwestern Ohio is con- 
cerned, it appears to have entered from some northern or north- 
western source. 
Strophomena concordensis-huronensisj var. nov. 
{Plate II, Figs. 1 A, B, C, D, E, F, G, H, J, K) 
In the Richmond group on Manitoulin Island, a species of 
Strophomena is very common at various levels between the Heh- 
