684 



NORTH AMERICAN INDEX FOSSILS. 



Like P. multisinuatum;hx\\. with compressed or carinated periph- 

 ery and very oblique aperture. 



Hamilton of New York, Ontario, etc. ; Sellersburg of Indiana. 



247. P. symmetricum Hall. (Fig. 964.) Devonic. 

 Like P. erectum, but only apically coiled ; margin sinuous. 

 Hamilton of New York, etc. 



248. P. thetis. (Fig. 963, d.) Devonic. 



b d 



Fig. 963. a, Platyceras erect urn ; b, P. caririatum ; d, P. thetis; e, P. bucculentum. 



(Copied from Hall.) 



More slender than preceding and strongly plicate. 



Hamilton of New York, Ontario, etc. ; Sellersburg of Indiana. 



249. P. bucculentum. (Fig. 963, e.) 



Devonic. 



Rapidly enlarging, lip strongly sinuate, 

 especially on one side. 



Hamilton of New York, Ontario, etc. ; 

 Sellersburg of Indiana. 



250. P. nodosum Conrad. (Fig. 965.) 



Devonic. 



Like P. gebliardi when young, but 

 with last volution bearing numerous strong rounded nodes. Adult 

 molds generally without coiled young, and strongly nodose. 

 Helderbergian and Oriskanian of New York, etc. 



251. P. dumosum Conrad. (Fig. 966.) Devonic. 

 Coiled only apically, rapidly expanding, numerous nodes (in 



molds) and hollow spines corresponding to them. 



Onondaga of New York and Ontario ; Columbus of Ohio and 

 Michigan ; Jeffersonville of Falls of the Ohio. 



252. P. vomerium Winchell. Mississippi. 



Fig. 964. Platyceras symme- 

 tricum. (Copied from Hall.) 





