416 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



PlatystrojjJiia foerstei, new species, of the Arnlieini formation has 

 the same general physiognomy, but the hitter species is usually nar- 

 rower and has a deeper sinus than this variety. 



Measurements. — 25.3 mm. along the hinge line, 22 mm. wide across 

 the middle, 15.5 mm. high, 12.3 mm. tiiick, 10 mm. sinal width, 5 mm. 

 sinal depth, 1.9 mm. fold depth. 



Occurrence. — Trenton group: Catheys limestone: Nashville, Wil- 

 jiamsport, Columbia, and Maury County, Tennessee. 



Coty pes. —Ca.t. No. 65985, U.S.N.M. 



PLATYSTROPHIA PRECURSOR ANGUSTATA. new variety. 



Plate 44, figs. 13-16. 



A small number of individuals may be selected from among the 

 typical specimens wliich are narrower, thicker, and have a higher, 

 more compressed fold. They have the physiognomy of Platystraphia 

 moritura Cumings, of the Upper Richmond of Kentucky, Indiana, and 

 Ohio, but arc, however, narrower, have a shallower sinus and some- 

 what rounder plications. 



Measurements. — 24.3 mm. along the liinge line, 25.5 mm. wide 

 across the middle, 18. 7 mm. high, 17.5 m.m. tliick, 13 mm. sinal 

 width, 10 mm. sinal depth, 45 mm. fold depth. 



Occurrence. — Trenton group. Catheys limestone: Nashville, Co- 

 lumbia, and Tullahoma, Tennessee. Prosser limestone: Hader, 

 Goodhue County, Minnesota (referred to this variety doubtfully). 



Coty pes. —Cat. Nos. 65888, 65890, 48642, U.S.N.M. 



MAYSVILLE AND RICHMOND SPECIES. 



PLATYSTROPmA JUVENIS, new species. 



Plate 43, figs. 36^1. 



This is a sub-equally convex transverse species with a low fold 

 bearing four plications which originate by the bifurcation of two pri- 

 mary plications at the beak, and with a shallow sinus which bears thi'ee 

 plications, of which one is primary and occupies a median position, 

 and two are secondary implanted plications occupying lateral posi- 

 tions on the sinal slopes. The lateral slopes of the brachial valve 

 are flatly convex and those of the pedicle valve flatly convex and 

 those of the pedicle valve flatly concave. They bear seven and eight 

 plications. The hinge hne is generally somewhat less than the width 

 across the middle but may equal tliis width. The cardinal areas nar- 

 row rapidly toward the cardinal extremes. The shell varies from 

 thin to strongly convex. 



PlatystropTiia juvenis resembles Platystropliia pauciplicata. Typi- 

 cal specimens are readily distinguished from that species by the more 

 numerous and more closely spaced plications, and by the absence of 

 curved lateral plications. 



