436 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56 



The slopes of the brachial valve have a.strongly convex curve from 

 the cardinal to the frontal margin. There is only a slight convex 

 curve from the fold to the lateral margins. The slopes of the pedicle 

 valve are strongly concave, the greatest concavity being behind the 

 cardinal angles. Specimens with fewer lateral plications which are 

 found associated with those just described are placed in this species 

 as they are in agreement in all other characters. 



Doctor Foerste has applied the name Platystro2)Ma cypJm conradi 

 (see pi. 47, figs. 26, 27, Cat. No. 66028, U.S.N.k.) to that type of shell 

 which is much prolonged along the hinge-line, bears numerous plica- 

 tions on the lateral slopes, and has a less compressed fold and sinus 

 which beai-s stronger lateral plications than is found in typical speci- 

 mens of Platystrojiliia cypha. 



PlatystropJiia cypha resembles PlatystropJiia unicostata and Pla- 

 tystropMa unicostata cras.nformis. The chief difference lies in its 

 greater width and correspondingly greater number of plications on 

 the lateral slopes. 



Measurements. — 33 mm. along the hinge, 25.5 mm. wide across the 

 middle, 17.5 mm. high, 17.5 mm. thick, 13.5 imn. sinal width, 11.5 

 mm. sinal depth, 6 mm. fold depth. 



Occurrence. — Richmond group: Arnheim formation: Waynesville 

 and Lebanon, Ohio; Seatonville, Bardstown, Lebanon, near Spring- 

 field, Fisherviile, etc., Kentucky; and Madison, Indiana. 



Plesioty pes. —C&t. Nos. 66001, 66009, U.S.N.M. 



PLATVSTUOPHIA CYPHA TUMLDA. new variety. 



Plate 48, figs. 17-20. 



Among the specimens of PlatystropMa cypha found in the Arnheim 

 of Tennessee, Kentucky, Ohio, and Indiana occurs a variety with a 

 tumid shell in which the thickness equals the width across the middle 

 and equals or exceeds the height. The hinge line forms the greatest 

 width. Four specimens from Mount Washington, Kentucky, have 

 the hinge line greatly extended but in most specim.ens it is about a 

 third greater than the width across the middle. The fold is high and 

 slightly less compressed than in typical specimens of the species. 

 The sinus is profound in front and has a du'ection at right angles to 

 the direction of the posterior portion of the sinus. The lateral plica- 

 tions of the fold and sinus are on the average relatively strong but 

 they are alwaj's weaker than the median plications. The number of 

 plications on the lateral slopes vary from 8 to 10. 



The slopes of the bracliial valve are swollen. The descent in all 

 directions is abrupt, but it is most abrupt toward the cardinal margin. 

 The lateral slopes of the pedicle valve are greatly elevated next to 

 the sinus. Strong compression of this valve has resulted in a decid- 

 edlv concave outline. 



