420 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



This species consists of specimens of the PlatystropMa 'precursor 

 type, but differs in having a slightly liigher fold and in having seven 

 instead of nine plications on the lateral slopes. 



Measurements. — 29 mm. along the hinge line. 27 mm. wide across 

 the middle, 17.5 mm. high, 14.5 mm, thick, 14.5 mm. sinal width, 

 7.2 mm. sinal depth, 4.5 mm. fold depth. 



Occurrence. — Maysville groujK Up])er Fairmount to Corryville 

 beds; Cincinnati, Oliio, and Madison, Indiana. 



Coty pes.— Cat. Xo. 65941, T.S.X.M. 



PLATYSTROPHIA ACUMINATA James. 



Plate 46, figs. 5-8. 



Orthis {Plutystrophia) acwninata James, Paleontologist, vol. 1, 1878, p. 7. 

 Platystrophia acuminata Foerste. Bull. Sci. Lab. Denison Univ., vol. 16, 191*, 

 pi. 6, fig. 13. 



Tliis is a thin form with acuminate liinge extremities. The fold 

 is moderately elevated and compressed, and the lateral plications on 

 the slopes of the fold and sinus are weak. Seven to 10 })lications 

 occupy the lateral slopes. 



Measurements.— V.) mm. along the hinge line, 13 mm. wide across 

 the middle, 9.5 nmi, high, 7.5 mm. thick, 7 mm. sinal width, 5 mm. 

 sinal depth, 3.7 mm. fold height. 



Occurrence. — Richmond group: Arnheim formation; Waynesville, 

 Ohio, and various localities in Kentucky. 



Plesiotype.—Csit. Xo. 65929, IT.S.X.M. 



PLATYSTROPHIA FOERSTEI, new species. 



Plate 46, figs. 9-12. 



This species has transverse equiconvex, thin valves with a hinge 

 line formmg the greatest width and with a low spreading fold and 

 shallow sinus which bear subequal plications. The lateral slopes of 

 the brachial valve are flatly convex, those of the pedicle valve 

 flatly concave. 



There are generally three plications in the sinus and four on the 

 fold, but this species in common with all other species which have 

 low spreading folds, shows a tendency to add tertiary plications bj 

 inplantation in the sinus and bifurcation on the fold. There are 

 8 to 10 plications on the lateral slopes. 



PhtystropJda foerstei resemble PlatystropTiia precursor latiformis 

 of the Upper Trenton. It has a slightly deeper sinus than the latter 

 form and the lateral slopes next to the sinus are somewhat higher. 



Measurements. — 19 mm. along the hinge line, 16.8 mm. vv^ide across 

 the middle, 12.7 mm. liigh, 9.4 mm. thick, 9.1 mm. sinal width, 5.3 

 mm. sinal depth, 3 mm. fold depth. 



Occurrence. — Richmond group : Waynesville, Ohio, Versailles, Indi- 

 ana. Arnheim formation: Branch Run, one mile east of Seatonville, 



