08 PALEONTOLOGY OF NEW YORK. 



This slit'll bears some resemblance to the more extravagant forms of Pterinea 

 flabclla, Imt it is larger than any known specimen of that species, with a ]n(i]tor- 

 tionallv longer and less defiiicil body, and distinctly dilTcrcnt surface ornamen- 

 tation. 



Formation and localiti/. In tiie upper beds of the Chemung group at Mansfield. 

 Tioga county, Penna. 



Pterinea Chemungensis. 



I'l.ATK XVI, FIGS. 3, 7, 10, 12; PLATE LXXXIV, FIU. 21. 



Arkula C'litiinunj, ii.-<i.s, Coxrad. Jour. Acad. Nat. Sci., Phila., vol. S, p. 243. 1842. 

 Anciiln jx'Henifuniiis, Hall. fSeolog-. Siirv. N. Y.: Kept. Fourth Dist., p. 262. 1843. 



Pteriiua CheiaimgensU, (Co.nrad) Hall. Pal. N. Y., vol. v, pt. 1. Plates ami Kxplaiuitioiis : PI. 10, fi-rs. 3, 



7, 10, 12. Jan., 1883. 



Shell very large, rhnuilioidal ; body of shell ovate, narrower jibove, nearly 

 erect, or sometimes oliii(|uc: IniLitli less than the height; greatest length 

 below the middle : basal ami post-liasal margins rounded; the anterior 

 margin above the iniildle is ueai-ly straight. an<l the corresponding portion of 

 the posterior margin is gently concave. 



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

 Right vah c depressed-convex towards the ])eak, flat or slightly concave below. 



Ilinge-liue straight, central ; length nearly or quite equal to the length of 

 the shell. 



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

 Uml)onal regiim not .strongly defined, most jirominent a little below the 

 hinge ; subtending an acute angle. 



Ear short, nearly e(|uilateral. limited by a rounded sulcus ; margin concave, 

 witli 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 l)y marked change in the surface characters 

 from the body of the shell ; margin straight or .slighth- concave ; extremity 

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

 left. 



Test .sonicwliiit thin; left valve marked by slendt-r. lililDrni ravs, varionsh 



