58 
Aug. F. Foerste 
the beak; partly it is due also to the greater convexity of the 
sides of the valve, anterior to the postero-lateral angles. The 
umbonal part of the pedicel valve, anterior to the beak, appears 
less elevated, and the general appearance of the posterior half of 
the valve is somewhat flatter. 
The interior of the valves is very similar to that of Strophomena 
sulcata. It is strongly striated radially, owing to the thinness of 
the shell. The muscular area of the pedicel valve is circular, it 
is well outlined laterally but not anteriorly. The two-lobed car- 
dinal process, the divergent crural plates, and the median ridge, 
extending forward from the callosity immediately anterior to the 
cardinal process, are well developed on the interior of the brachial 
valve. The diductor area is poorly defined. 
Strophomena sinuata was described from the upper part of the 
Fairmount, at Cincinnati, Ohio, at a horizon which is a consider- 
able distance above the Strophomena planoconvexa level, at the 
base of the Fairmount. It occurs also at Madisonville, Ohio. 
At Bald Hill, 1 mile west of Georgetown, in Brown county, Ohio, 
Strophomena sinuata is not rare at a horizon 45 feet above that 
part of the section, feet thick, in which Strophomena maysvilt- 
ensis is common. A few specimens of Strophomena planoconvexa 
occur both above and below this Strophomena sinuata horizon 
for a distance of 10 feet. At Bald Hill, the specimens of Stropho- 
mena sinuata have an appearance as though they might have been 
derived from some nasute form of Strophomena maysvillensis; 
in other words, as though they might be depauperate specimens 
of the latter. Strophomena sinuata occurs also as an occasional 
loose specimen west of Mount Sterling, 3 miles north of Vevay, 
in Switzerland county, in Indiana. A single specimen, resembling 
Strophomena sinuata, was found 50 feet above the base of the 
section in which Strophomena maysvillensis is very common, and 
which here is regarded as at the base of the Fairmount. 
Strophomena sinuata, although resembling Strophomena mil- 
lionensis, certainly was not derived from that species. It has 
been found so far only near the upper limits of the range of Stro- 
phomena maysvillensis. In Ohio and Indiana it is known only near 
the northern limits of the geographical range of that species. It is 
also listed by Ulrich from the Strophomena maysvillensis horizon 
in the Maury phase of the Fairmount, within the limits of the 
Columbia folio, in Tennessee. I have never seen any very t 3 ^ical 
