98 PALAEONTOLOGY OF NEW YORK. 



This shell hears some resemblance to the more extravagant forms of Pterinea 

 flabella, but it is larger than any known specimen of that species, with a propor- 

 tionally longer and less defined body, and distinctly different surface ornamen- 

 tation. 



Formation and locality. In the upper beds of the Chemung group at Mansfield, 

 Tioga county. Penna. 



Pterinea Chemungensis. 



PLATE XVI, FIGS. 3, 7. 1". 13; PLATE I.XWIV, FIG. 21. 



a Chemii igensis, Cohrad. Jour. Acad. Nat. Sci., Pliila., vol. S, \>. 243. 1S42. 

 .1.;, ,> peeteiiifonnis, Hail. Geolog. Surv. N. Y.x Rept. Fourth Dist., p. 262. 1843. 



inta Cltemwigensis, (Conrad) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 16, figs :!. 



7, 10. \i. Jan.. 1SS3. 



Shell very large, rhomboidal; body of shell ovate, narrower above, nearly 

 erect, or sometimes oblique; length less than the height; greatest length 

 below the middle : basal and post-basal margins rounded; the anterior 

 margin above the middle is nearly straight, and the corresponding portion of 

 the posterior margin is gently concave. 



Left valve moderately convex above, depressed-convex in the lower part. 

 Right valve depressed-convex towards the beak, Hat or slightly concave below. 



Hinge-line straight, central : length nearly or quite equal to the length of 

 the shell. 



I teak anterior, acute, directed forward, arching a little over the hinge-line. 

 Umbonal region not strongly defined, most prominent a little below the 

 hinge; subtending an acute angle. 



Ear short, nearly equilateral, limited by a rounded sulcus ; margin concave, 

 with a marked sinuosity and arching of the shell for the byssal sinus. Wing 

 large, triangular, and extending beyond the posterior margin of the valve, not 

 distinctly defined by a sulcus or by marked change in the surface characters 

 from the body of the shell: margin straight or slightly concave; extremity 

 obtuse. In the right valve, the wing is less distinctly defined than in the 

 left. 



Test somewhat thin; left valve marked l>v slender, filiform rays, variously 



