GASTROPODA— STROPHOSTYLID&. 689 



Louis of Indiana, Illinois ; Chester of Arkansas ; Coal measures 

 of Pennsylvania. 



LXXVII. Igoceras Hall. 



More or less broadly conical platyceroids with apex not in- 

 curved ; body portion plicate. (Probably a polyphyletic group.) 

 Devonic-Carbonic. 

 265. I. plicatum (Conrad). (Fig. 978.) Devonic. 



Apex sublateral, one side more strongly curved; height about 



Fig. 978. Igoceras plicatum. (After Fig. 979. Igoceras conicum. (After 

 Hall.) Hall, Pal. N. Y., V.) 



one and one half times greatest diameter ; plications few and 

 shallow, generally only on straight side. 

 Helderbergian of New York, etc. 



266. I. conicum (Hall). (Fig. 979.) Devonic. 

 Irregularly conical, with apex pointed and subcentral or excen- 



tric ; height equal to or less than basal diameter ; plications strong, 

 rounded, sometimes obsolete. 



Onondaga and Hamilton of New York, Ontario, and Falls of 

 Ohio. 



267. I. capulus (Hall). (Fig. 980.) Mississippi. 

 Subregularly conical, with nearly central apex ; a slight flatten- 

 ing and very faint undulations occur on one side ; height less than 

 basal diameter ; aperture nearly circular. 



Burlington of Iowa, Missouri, and Illinois. 



