32 NORTH AMERICAN INDEX FOSSILS. 



lo-f. Lateral saddle prominent, flanked by sharp lobes on each 



side k. 



h. Lateral saddle broad, round... LXXVIL Manticoceras. 



h. Lateral saddle sharp d/ . 



4''. Broadly umbilicated LXXVIII. Probeloceras. 



4^. Minutely umbilicated or non-umbilicate F. 



F. Ventral saddle with simple notch. 



LXXXII. Gonioloboceras. 

 F. Ventral saddle with complex lobing resulting in 

 several narrow lobes and saddles. 



LXXXIIL Dimorphoceras. 

 lof . Lateral saddle and superior lobe alone present on side of 



shell, the second lobe at umbilical margin i. 



i. Shell with pronounced umbilicus with angular margin. 

 LXXXL Muensteroceras, 

 i. Umbilicus minute or closed ; shell subglobose. 



LXXXIV. Goniatites, 



I of. Lateral saddle equal to or less prominent than superior 



lateral one ; superior lateral and second lobe both 



present .^ 



j. Broadly umbilicated 5' 



5^. Ventral saddle mostly low or absent ; whorls ver- 

 tically compressed LXXXV. Glyphioceras. 



5''. Ventral saddle moderate or high 



g''. Shell with ribs or tubercles on side. 



LXXXVL Gastrioceras. 

 g''. Shell smooth, whorls scarcely embracing. 



CL Paralecanites. 

 j. Umbilicus narrow, but deep, shoulders flat. Shell hel 

 met- shaped with constrictions or varices. 



XCVI. Nanniies. 



jj. Ventral saddle undivided 



Il|. Whorls laterally compressed 



k. Lobes and saddles angular. ..LXXXII. Gonioloboceras. 



k. Saddles rounded, long and narrow 6 



6''. Ventral saddle bottle-shaped. 



LXXXVII. Schistoceras. 

 6^ . Ventral saddle not bottle-shaped. 



LXXXVII I. Faralegoceras. 

 I if. Whorls vertically depressed ; umbilicus large. 



LXXXVL Gastrioceras 

 2. Suture simple (goniatitic) only in young ; in adult, one or more of the lobes 



are modified by secondary notches or serrations (ceratitic suture) 5*. 



5*. Lobes numerous and similar, serration bifid or trifid j 



j. Shell slightly compressed or subglobose 777' 



777. Umbilicus almost closed .LXXXIX. Popanoceras 



777. Umbilicus rather wide kk, 



kk. Siphonal saddle bottle-shaped XC. Shumardites. 



kk. Siphonal saddle not bottle-shaped. 



LXXXIXA. Parapopanoceras. 



