690 



NORTH AMERICAN INDEX FOSSILS. 



Fig. 980. Igoceras capulus. (After Keyes. ) 



268. I. quincyense (McChesney). (Fig. 981.) Mississippic. 



Height nearly equal to basal diameter ; lower half deeply and 

 coarsely plicate ; apex subcentral. 



FlG. 981. Igoceras quincyense, at- 

 tached to calyx of crinoid. (After 

 Keyes. 



Fig. 982. 

 Keyes. ) 



Igoceras fissurella. ( After 



Burlington of Illinois, Iowa, and 

 Missouri. 



269. I. fissurella Hall. (Fig. 982.) 



Mississippic. 



Higher, somewhat more strongly 

 plicate, and with more excentric apex 

 than /. capulus. Aperture more sin- 

 uate. 



Burlington of Iowa ; Keokuk of 

 Illinois. 



270. I. pabulocrinus 



Owen. (Fig. 983.) 



Mississippic. 

 Like /. fissurella, but 



Fig. 983. Igoceras pabulocrinus . . . ... 



more slender and with at- 



Bs 



Fig. 984. 

 Igoceras sub- 

 on Platycrinus hemisphericus. (Aft- iii ^ iV ' «*>-««>" «.*.»-• ,, ^** **». pUcatum. 



er Keyes.) tenuated, often bent apex ; (After Keyes.) 



