88 NORTH AMERICAN INDEX FOSSILS. 



shallow, dorsal lobes, generally with slight, median, dorsal saddle; 

 septa creased or raised into a median ridge between the two sad- 

 dles ; siphuncle centren or slightly excentric. Carbonic. 

 103. E. divisum (White and St. John). Carbonic. 



Large (living chamber 195 mm. long by 200 mm. wide), strongly 

 flattened dorso-ventrally to half the transverse diameter or less; 



Fig 1306 Apheleceras disci for me, nearly complete specimen, X ^A > ^i^h view 

 of inner side of septa, X K» ^"^^ transverse section, X /i' (After Meek and Worthen, 

 111. Gaol., V.) 



venter with faint depression or flattening; increase in width very 

 rapid. 



Lower Coal Measures of Kansas, Missouri and Texas; Upper 

 Coal Measures of Iowa. 



104. E. f erratum (Cox). Carbonic. 



Much smaller than preceding, whorls less strongly compressed, 

 enlargement of whorls less rapid; umbilicus profound, with nearly 

 vertical walls. 



Coal Measures of Arkansas and Kentucky. 



XXXIV. Triboloceras Hyatt. 



Gyroceracones and nautilicones in form, similar to preceding 

 genera, but venter channeled only in young, when the shell is also 

 characterized by subspinous ridges; adult whorls more or less 

 depressed, biangular with gibbous dorsum and convex venter, or 



