CEPHALOPODA— ORTHOCHOANITES. 89 



approximately triangular with concave abdomen. Siphuncle above 

 center; sutures with broad ventral and lateral lobes, and dorsal 

 saddles without annular lobes. Mississippic. 



105. T. digonum (M. and W.). (Fig. 1307.) Mississippic. 



Venter broadly convex, with shallow lateral concavities and pro- 

 nounced lateral angles. Surface with revolving striae. 



Fig. 1307. Tribolocer as digonum. (After Meek and Worthen, 111. Pal., II. ) 



Rockford Goniatite bed of Indiana; Kinderhook of Illinois and 

 Missouri. 



XXXV. Stearoceras Hall. 



Nautilicones with adult considerably involute, with deep, narrow 

 umbilicus, broad, smooth, rounded venter, shallow ventral lobe and 

 small dorsal and annular lobes. These features distinguish it from 

 Endolobus. Carbonic. 



106. S. gibbosum Hyatt. (Fig. 1308.) Carbonic. 



Rapidly enlarging whorls of broadly rounded, nautilian aspect 

 with deep hyponomic sinus. 



Carbonic of Texas. 



XXXVI. Leuroceras Hyatt. 



Similar to preceding, but with ventral saddle instead of lobe, the 

 young striate in typical forms. Mississippic-Carbonic. 



