96 
Aug. F. Foerste 
of the Blanchester division of the Waynesville bed, the evident 
precursors of this species are not uncommon locally. Here they 
are associated with Strophomena neglecta. From the latter species 
they may be distinguished readily by the deflection of the lateral 
borders of the muscular area toward the front, leaving a median 
gap; by the tendency toward perpendicular wrinkling at the 
hinge-line ; and by the irregular concentric wrinkling of the pedicel 
valve, accompanied by a corresponding deviation of the radiating 
striae from their usual straight-line directions. 
Compared with the typical forms of Strophomena vetusta, from 
the Whitewater bed, the variety precursor usually has less prom- 
inent radiating striae on the brachial valve, even in cases where 
the number of striae is approximately the same. Frequently, 
however, the number of these striae equals 10 to 13, in place of 8 
to 10, in a width of 5 mm. The area of the pedicel valve usually 
is not so conspicuously elevated, and the perpendicular wrinkling 
along the hinge-line usually is less in evidence. The four parallel 
ridges and intermediate vascular sinuses along the median parts 
of the interior of the brachial valve are less conspicuous. The 
interior of the valves is more minutely pustulose. In other words, 
the variety precursor differs but slightly from the typical White- 
water forms of Strophomena vetusta. The valves are thinner and 
less robust. Their chief interest lies in their earlier occurrence. 
The types of the variety precursor were found in the Blanchester 
division of the Waynesville bed, along Penquite Bun, two and a 
half miles west of Clarksville, Ohio, south of the pike, above the 
lower Hehertella inscutpta horizon. 
Strophomena vetusta-precursor occurs usually above the middle 
of the Blanchester division of the Waynesville member. It fre- 
quently is associated with Strophomena neglecta, especially in the 
lower part of its range, but at Moores Hill, in Dearborn county, 
Indiana ; a mile and a half southwest of Oxford, in the northwest- 
ern part of Butler county, Ohio; at Oregonia, in Warren county; 
at Clarksville, in Clinton county; and at Concord, in Lewis 
county, Kentucky, its vertical range extends above that of 
Strophomena neglecta. At Moores Hill, its vertical range equals 
11 feet, but usually it does not exceed 2 or 3 feet. 
Its most southern range extends to Owingsville, in Bath county, 
Kentucky. Specimens are found also at Concord, in Lewis 
county; and on Eagle Creek, four miles west of West Union, in 
