12 • PALEONTOLOGY OF NEW YORK. 



This species is conspicuously different from the P. dumosum in the shorter 

 and comparatively equilateral and more expanded form ; while the few scattered 

 lobular spines appear to he disposed without order on the surface. A variety 

 (figs. 8 and 9 of pi. 5), which may helong to this species, has a less expansion of 

 aperture, an ohliquely ovoid form, less attenuate apex, and greater proportion- 

 ate height. 



Formation and localities. In limestone of the Upper Helderberg group, at 

 Williamsville, and near Carlisle, N. Y. The varieties are from Darien, N. Y. 



Platyceras cymbium. 



PLATE IV, FIGS. 9-11. 



Platycera* cymbium, Hall. Descriptions of New Species of Fossils, etc., p. 7. 1861. 

 " " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 85. 1862. 



" " " Illustrations of Devonian Fossils : Gasteropoda, pi. 4. 1876. 



Shell subangularly ovoid. Apex minute, making one or more turns, below 

 which the shell is abruptly expanded ; the back flattened or but moderately 

 convex, while the right side is distinctly flattened, making an obtuse 

 angular ridge between the side and back of the shell : sloping more gently 

 on the left side and becoming regularly convex. Aperture widely ex- 

 panded. 



Surface marked by transverse stria?, which are undulated on the dorso-lateral 

 angle. Shell lamellose striate. 



This species is characterised by the broad expansion of the aperture, the 

 usually flattened dorsum, and the abrupt right or upper side, giving an obtuse 

 dorso-lateral angle. 



A careful examination of specimens renders it quite doubtful whether any 

 of those with scattered spines really belong to this species. 



Formation and locality. In Upper Helderberg limestone, at Clarence Hollow, 

 N. Y. 



