48 
Aug. F. Foerste 
process, and the anterior extremities of the crural plates. The 
latter curve rather strongly forward. A low median ridge extends 
forward from the cardinal process, between the adductor areas. 
Anterior to a line connecting the anterior margins of the adductor 
areas, there frequently is a median depression, bounded laterally 
by the inner pair of vascular ridges which are parallel to the median 
parts of the shell. The narrow posterior extension of this inner 
pair frequently may be distinguished from the median ridge 
which extends forward from the cardinal process. The outer 
pair of vascular ridges is low, broad, and rather indistinct, ter- 
minating posteriorly at the anterior margin of the adductor areas. 
The radiating striae on the exterior surface are rather coarse, 
agreeing in this respect with those of Strophomena planoconvexa. 
On the pedicel valve, 10 to 12 striae occur in a width of 5 mm. 
about 25 mm. from the beak. The same number of striae occur 
on many of the brachial valves, but here sometimes 14 and 15 
striae are found in the same width. Frequently the striae appear 
coarser along the middle and posterior parts of the shell, becoming 
finer and less conspicuous along the anterior margin of the shell. 
In the younger stages of growth, the postero-lateral angles 
of the shell are more nearly rectangular. In adult specimens 
these angles often are more or less rounded, and the posterior part 
of the lateral outlines converges slightly toward the hinge-line. 
The type specimens of Strophomena maysvillensis were found 
in the lower part of the Fairmount bed, along the railroad, 2 miles 
southeast of Maysville, Kentucky. 
At Maysville, in Mason county, Kentucky, the base of the 
Fairmount is placed at the base of the strata in which Stropho- 
mena maysvillensis is most abundant. This part of the section 
is 18| feet thick. It consists, near the base, of fairly massive 
limestone, weathering, toward the top, to shaly limestone inter- 
bedded with more solid layers. The overlying argillaceous rock 
section, about 50 feet thick, is nearly unfossiliferous, and is corre- 
lated with the Tate layer, typically exposed in Madison county. 
Beneath the Fairmount, Strophomena maysvillensis is found in 
small numbers down for a vertical distance of 22 feet, in strata 
regarded as corresponding to the Mount Hope member, typically 
exposed at Cincinnati. 
A similar distribution of Strophomena maysvillensis in the Mount 
Hope and Fairmount members has been noted as far south as 
