682 



NORTH AMERICAN INDEX FOSSILS. 



238. P. multisinuatum Hall. (Fig. 958.) Devonic. 



Like a small P. gebhardi, with longitudinal folds and strongly 



Helderbergian of New York. 

 239. P. unguiforme Hall. (Fig. 959, a-c.) 



Devonic. 



Fig. 959. a-c, Platyceras unguiforme var. multicarinatum ; b, P. unguiforme ; 

 d-f P. di/atatum, showing varieties (e,f, opposite views of same specimen). (Pal. 

 N. Y., III.) 



Like preceding, but mostly non-coiling. 

 Helderbergian of New York. 



240. P. dilatatum Hall. (Fig. 959, d-f.) 



Devonic. 



Like P. tenuiliratum, but only apex coiled; 

 sometimes carinate. 



Helderbergian of New York. 



241. P. spirale Hall. (Fig. 960.) Devonic. 

 Non-coiling except at apex, but with a 



few irregular twists ; somewhat plicate. 



Helderbergian of New York. (A more 

 slender, less plicate form occurs in the 

 Oriskany (P. tortuosum), and a similar one 

 making only half a twist [P. dentaliuni) in 

 the Onondaga of New York.) 



. 242. P. magnificum Hall. (Fig. 961.) 



FlG. 960. Platyceras spi- ^ b \ t> * / 



rale. (After Hall.) DevoniC. 



