406 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



occupied by the fold and sinus is reentering, the depth of the incurvation being about 

 equal to the elevation of the umbo above the hinge line. The depressions of the sinus 

 is occupied by only two plications and the ridge by three similar folds. On either side 

 are from eight to nine plications. The numbers seem invariable. 



The muscular area of the toothed valve is long and narrow, length being three or 

 four times the width, extending nearly to the center of the valve — a feature in which 

 this species differs from its representatives. 



Occurrence. — Gamachen (Ellis Bay) and Aiiticostian (Gun River) 

 Junction Cliff, etc., Anticosta. 

 Plesiotype.— No. 66108, U.S.N.M. 



PLATYSTROPHIA DAYTONENSIS (Foerste). 

 Plate 42, fig. 24. 



Orthis biforata var. lynx forma daytonerisis Foerste, Bull. Sci. Lab., Denison 



Univ., 1, 1885, p. 81, pi. 13, figs. 1-8. 

 Orthis (Platystrophia) biforata (part) Foerste, Geol. Surv. Ohio, vol. 7, 1895, p. 



579, pi. 25, fig. 8. 

 Platystrophia daytonensis Savage, Bull. Geol. Surv. Illinois, vol. 23, 1913, p. 76, 



pi. 4, fig. 8. 



The shell is small, wider than long with a subquadrate outline. 

 The hinge line about equals the width across the middle. The fold 

 bears three plications. Two originate in a point at the beak, the 

 third is intercalated in a median position when the shell is about 1 

 mm. long. There are two plications in the sinus. As the posterior 

 portion of the pedicle valve of the one specimen was broken away 

 nothing definite can be said as to their origin, but it is inferred from 

 other specimens which have a like plication pattern on the fold, that 

 the two originate by the bifurcation of a primary plication at the 

 beak. The lateral slopes are occupied by nine roundish plications 

 which are separated by their own width. 



Measurements. — 18.5 mm. along the hinge line, 18.5 mm. wide 

 across the middle, 14.2 mm. high, 13 mm. thick, 8 mm. sinal width, 

 6.7 mm. sinal depth, 2.5 fold depth. 



Occurrence. — ^Brassfield formation, Dayton, Ohio; Hanover, In- 

 diana; Cumberland Gap, Tennessee; Collinsville, Alabama; Nelson 

 County, Kentucky. Edgewood formation; Edgewood and Louisi- 

 ana, Missouri; Theber, Illinois. 



Plesioty pes. --Ca,t. No. 66114, U.S.N.M. 



PLATYSTROPHIA DAYTONENSIS LAURELENSIS, new variety. 



Plate 42, figs. 42, 43. 



This variety is distinguished from the Brassfield specimens by its 

 smaller size and narrower form. 



Measurements. — 13 mm. along the hinge line, 14 ram. wide across 

 the middle, 12 mm. high, 11 mm. thick (estimated), 18 mm. sinal 

 width, 5 mm. sinal depth, 2 mm. fold height. 



