Richuwnd Group of Cincinnati Anticline. — Focrstc. 341 
Platystrophia acutilirata is a descendant of Platystrophia 
laticosta. The typical specimens of Platystrophia laticosta begin 
their appearance in the Bellevue bed, and thence continue 
through the remainder of the Lorraine stage into the Lower 
Richmond. In the Lower Richmond a part of the spec- 
imens show an increase in the number of lateral plications 
and a prolongation of the postero-lateral angles, features 
which find their most pronounced expression in Platys- 
trophia acutilirata. Platystrophia cypha from the Lower 
Richmond, is evidently one of the transitional forms in 
which the increase in the number of lateral plications and 
the prolongation of the postero-lateral angles has been accom- 
panied bv a reduction in the number of plications on the me- 
dian fold and in the sinus. 
Strophonicna planunibona occurs in the middle part of 
the Lower Richmond. Strophonicna subtcnta is found in the 
lower part of the Middle Richmond. Specimens intermediate 
between Strophonicna planunibona and Strophonicna subtcnta 
are found in the upper part of the Lower Richmond 
In typical specimens of Strophonicna subtcnta the thick- 
ening of the border around the anterior and lateral mar- 
gins of the interior of the shell is comparatively small. 
the muscular cavity is less prominently bordered, and the 
shell attains a larger size. The posterior . half of the dorsal 
valve is distinctively flattened and usually slightly concave 
anterior to the beak. The striations of the, ventral valve are 
about ecjual in size to those of the dorsal valve. Strophonicna 
vctusta dififers from Strophonicna siitjtcnta in the nnich smaller 
and more even convexity of the dorsal valve, and in the very 
slight flattening of this valve near the beak. The radiating 
striations of the ventral valve are conspicuously finer than 
those of the dorsal valve. Moreover, the radiating striations 
of the ventral valve are crossed by fine concentric striations 
and wrinkles which are usually readily seen, especially on the 
posterior half of the shell, and are very characteristic of this 
species. As a rule, the cardinal area of the ventral valve is 
much higher at the beak in Strophotnena vetusta than in 
Strophomena subtcnta. I am under great obligations to pro- 
fessor Stuart Weller for the opportunity of examining the type 
specimens of Strophonicna vctusta in Chicago Univei««ity. 
