NO. 2297. BRACHIOPOD GENUS PLATYSTROPHIA—McEWAN. 409 



Bomewhat sinuously rounded at the junction of the mesial sinus and fold. Beaks 

 nearly equal, incurved and approximate, sometimes almost touching; cardinal areas 

 nearly equal. 



Dorsal valve more convex than the ventral, its greatest convexity being near the 

 middle. Mesial fold rather rounded, arising near the beak, becoming more prominent 

 as it extends forward, with rounded sides; beak projecting beyond the hinge margin, 

 strongly incurved; cardinal area directed backward, somewhat incurved; foramen 

 broad, triangular and not closed )jy the cardinal process. 



Ventral valve of a mesial sinus, beginning near the beak, extending forward, ter- 

 minating in a rounded projection which continues the curvature of the shell and thus 

 produces a sinuous outline for the front edge of the shell. Surface of the valve rounded 

 into the .moderately concave sinus. Beak less strongly incurved than that of the 

 dorsal valve. Cardinal area incurved and directed backward, less, however, than that 

 of the other valve. Foramen triangular, wider than high; hinge teeth moderately 

 prominent and trigonal ; muscular cavity oblong, little more than one third the length 

 of the shell, lateral margins parallel, well defined by the dental ridges. On either side 

 of this cavity are a number of short striae, which are arranged Ln longitudinal lines 

 following about the direction of the plications. 



Surface of each valve with rounded, radiating plications, from 24 to 36 in number, 

 of which 4 to 6 occupy the mesial sinus, and 5 to 7 (in one specimen 10 or 11) the mesial 

 fold. In the sinus two plications begin at the beak, two additional ones are immedi- 

 ately added, and later one or two more at one-third or one-half the length of the shell 

 from the beak. On the mesial fold three plications originate at the beak, to which 

 two more are added at one-fourth the length of the shell from the beak; later two more 

 appear and in one specimen in hand 10 or 11 plications are more or less distinctly 

 shoAvn. The plications in the sinus and on the fold branch in all specimens as described 

 above; the lateral ones, 10 to 15 in number, are almost always simple. Lines of 

 growth not shown in the specimens found. Well preserved specimens under the 

 microscope show numerous minute granules, arranged in regular rows across the 

 plications. 



Occurrence — Brassfield limestone; Dayton, Ohio. 

 Plesiotype.—Csit. No. 48626 U.S.N.M. 



d. STTBGROUP D. 

 PLATYSTROPHU HERMITAGENSIS, new species. 



Plate 42, figs. 15-19. 



This represents a species, the types of which were collected from 

 the Hermitage limestone of Auburn, Tennessee. It is a thin, long- 

 hinged form with subequally convex valves. The species resembles 

 Platystrophia extensa, new species, in general physiognomy, but the 

 latter belongs to the Triplicate Group. 



In the nepionic stage there is one plication in the sinus and two on 

 the fold which appear to originate in a point at the beak. The neanic 

 stage is initiated by the bifurcation of the plication in the sinus and 

 on the fold this development is marked by the intercalation of a 

 median secondary plication. After a slight interval of growth a 

 plication is intercalated in a median position in the sinus, and a little 

 later a plication is implanted on each of the sinal slopes, while on the 

 fold first the median plications and then the primary plications 

 bifurcate. 



