LAMELLIBRANCHIATA. 433 



Valves regularly convex below the middle, becoming gibbous above, some- 

 what depressed-convex, along the middle, from the umbo to the basal margin. 



Beaks at about the anterior third, prominent. Umbonal slope sub-angular 

 above, declining very abruptly to the post-inferior extremity. 



Surface marked by numerous fine rounded radii, with narrower inter- 

 spaces. The radii on the posterior slope are slightly stronger, and those on 

 the anterior are much stronger than those in the middle of the valve. Entire 

 surface marked by strong concentric undulating striae, which become fascicu- 

 late, and produce varices of growth below the middle of the shell. 



Ligamental area narrow. Hinge-line with numerous crenulations. 



Two specimens measure respectively 29 and 38 mm. in length, and 27 

 and 36 mm. in height. 



This species is distinguished by its erect rhomboidal form, and nearly equal 

 length and height. The radii are also finer than in P. venusta. 



Formation and localities. In the sandstones of the Waverly group, at Warren 

 and Meadville, Pa. 



CARDIOPSIS, Meek AND WoRTHEN. 1861. 

 Cabdiopsis radiata. 



PLATE LXX, FIG. iS. 



Cardiomarpha radiata, Mkbk and WoRXHBif. Proc. Acail. Nat. Sci., Pliila., p. 448. 1860. 

 CardivpgU " " Pal. Ills., vol. ii, p. 157, pi. 14, figs. 6a, 6i. 1866. 



" " " Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 



PI. 70, fig. 25. 1883. 

 Megambonia Lyoni, Hall. Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 110. 1860. 



The specimen figured is from the original locality, and is the type referred 

 to in the description of Megambonia Lyoni. It does not appear to be congeneric 

 with any of the forms occurring in the New York series. 



The species has much resemblance to Cardiomorpha ovata, B.ali.=: Dexiobia 



OVata, WiNCHELL.* 



Formation and locality. In the Kinderhook group at Rockford, Ind. 



* Dualhia, Bakkakdb, 1881, is apparently identical with Dexiobia, Winchkll, 1863. 



