646 



NORTH AMERICAN INDEX FOSSILS. 



with strong, often elevated transverse striae ; increasing by inter- 

 calation in last whorl. 



Schoharie grit and Onondaga of New York, etc. 



XLI. Mourlonia DeKoninck. 

 Umbilicated pleurotomarioids, with body of whorl large, shoulder 

 more or less flattened, forming conical or discoidal spire ; band 



Fig. 880. Spiroraphe arata. (After 

 Hall.) 



Fig. 881. Mourlonia mississippien- 

 sis. (After Meek, Pal. Ohio, II.) 



heavy just above the ambitus ; surface with spirals cancellating 

 the growth lines. Mississippic-Carbonic. 



137. M. mississippiensis (Wh. and 

 Whit.). (Fig. 881.) Mississippic. 



With nearly flat shoulders ; whorls 

 embracing to ambitus, generally cover- 

 ing band of preceding whorl. 



Kinderhook of Iowa ; Waverly of 

 Ohio. 



XLII. Gyroma Oehlert. 



Round-whorled pleurotomarioids or- 

 namented by revolving spirals and trans- 

 verse ridges. Band above the middle 

 Devonic. 



Fig. 882. Gyroma capilla 

 ria. (After Hall. ) 



