Strophomena and Other Fossils 
67 
The chief difference between the Manitoulin specimens and 
Strophomena concordensis consists in the presence of the oblique 
wrinkles along the hinge-line. In Strophomena concordensis, from 
Ohio and adjacent Kentucky, the outline of the shell more fre- 
quently becomes sub triangular ; when the shell is viewed from the 
side, the posterior flattened part of the brachial valve usually rises 
more abruptly above the plane passing through the margins of 
the valve; in consequence, the hump at which the downward 
flexure of this valve is greatest lies nearer the posterior part of 
the valve; the curvature from this hump toward the anterior 
margin usually is less, producing a long slope in this direction, 
with longer and somewhat flatter antero-lateral slopes, resulting 
frequently in the more triangular outline already mentioned. 
It should be emphasized, however, that the differences here noted 
are not characteristic of all the shells, and are not likely to be 
observed unless large collections of shells are at hand, in which 
case the general facies is that here described. 
The chief interest in these Manitoulin specimens lies in the 
fact that from the central type here described, including the vast 
majority of specimens, there is a line of variation towards speci- 
mens which can not be distinguished from Strophomena planum- 
hona, but which exist in much smaller numbers. A few speci- 
mens also show a line of variation toward Strophomena nutans. 
Individual specimens that can not be distinguished from typi- 
cal Strophomena planumhona, Strophomena planumhona-gerontica, 
and Strophomena nutans also occur. Why should these speci- 
mens always be isolated? 
It is not worth while comparing this species with Strophomena 
hecuha until the genus of that species is known. Its vertical 
range suggests Strophonella instead of Strophomena, and the inte- 
rior of this species has not been described so far. Provisionally, 
the absence of indistinct concentric wrinkles will be sufficient 
to distinguish all of the variations of the Strophomena concor- 
densis type. 
The type specimens of the variety huronensis occur in great 
abundance at the eastern end of Manitoulin Island, at the Clay 
Cliffs, 3 miles north of Wekwemikongsing. This is the locality 
long known as Cape Smith, although this Cape lies several miles 
toward the northward. The clay cliffs are best reached by the 
long walk over large boulders along the shore. Specimens of the 
