Lamellibranchiata. 285 



to the extremity which is angular. The extent of the ear is not 

 known, but it is limited by a deep sulcus which gives an angular 

 aspect to the antero-cardinal slope of the shell. Byssal sinus not 

 marked in the specimens. 



Surface ornamented with about fifteen broad, strong, rounded 

 rays, crossed by lamellae of growth. The specimens described are 

 weathered casts of the interior and preserve only slight evidence of 

 the surface characters. 



The largest specimen has a convexity of about 20 mm., its 

 length is 70 mm., height 65 mm., and hinge-line more than 65 mm. 

 Another example has a convexity of about 20 mm., length 63 

 mm., height 74 mm., hinge-line 55 mm. 



This species bears some general resemblance to P. flabella; it differs 

 in its large ventricose form, more elevated umbo, the characteristics 

 of the upper part of the anterior side of the body, and the abrupt 

 slope into the wing without a distinct sulcus. 



Formation and locality. In the Corniferous limestone, near Colum- 

 bus, Ohio. 



Pterinea flabella. 



Ameula tuberculata, Conrad . Geolog. Surv. N.Y.: Ann. Rep., p. 117. 1838. 



Amcula flabella, Conrad. Jour. Acad. Nat. Sci., Phila., vol. 8, p. 238, pi. 12, fig. 

 8. 1842. 



(") Vanuxei^ Geolog. Surv. N. Y. ; Rep. Third Dist., 



p. 152. 1843. 



Compare Pterinea fasciculatus, Goldfuss. Petrefacta Germanise, p. 137, pi. 120, 

 fig. 5. 1840. 



" " (") Sandberger, Verstein, Rhein, Schich- 



tensyst, Nassau, p. 293, pi. 30, fig. 7. 1856. 



Compare Pterinea costulata, F. A. Roemer, Dunker and von Meyer. Palaeon- 

 tographica, T. 1, fig. 2. 



Plerinea flabella (Conrad), Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 14, figs. 1-21 ; pi. 15, figs. 1, 4-6, 8-10. Jan., 1883. 



Shell large; body broad or narrow ovate, oblique, rarely erect; length 

 from two-thirds to nearly equal the height ; and in some extrava- 

 gant forms the height is about double the length; the greatest 

 length below the middle; anterior and basal margins regularly 

 curved ; the posterior margin from a little above the base, follows a 

 nearly straight line to the beak. Left valve more or less convex, 

 often gibbous and arcuate. Right valve flat or concave, with a little 

 convexity on the umbo; arcuate, to correspond with the curvature of 

 the opposite valve. Hinge-line straight, extended upon the poste- 

 rior side; length greater than the length of the valve. Beak of left 

 valve acute, rounded, situated near the anterior extremity of the 



