GASTROPODA— TROCHOTURBINIDJE. 



669 



Whorls embracing to ambitus ; suture slightly excavated ; 

 shoulder nearly flat; spirals comparatively simple, an intercalated 

 series occurring on the body whorl ; sharp oblique lines of growth, 

 often strongly marked and crowded. 



Richmond group of Indiana, Ohio, Illinois, and Minnesota. 



198. C. mediale Ulrich. (Fig. 925, c, d.) Ordovicic. 

 Whorls more ventricose than preceding, spirals coarser, suture 



shallow. 



Lower and Upper (C. humorosuni) Lorraine of Ohio, Kentucky, 

 and Indiana. In those of the upper beds, the whorls embrace 

 more strongly, the form becoming more compact and wider angled 

 (C humorosnm Ulrich, Fig. 925, e—g). 



199. C. varicosum Hall. (Fig. 925, //, i.) Ordovicic. 

 Round-whorled, primary spirals coarse, with several finer 



between. 



Trenton of Kentucky, Tennessee, Michigan, etc. 



200. C. sublaeve Ulrich. (Fig. 925, /.) Ordovicic. 

 Similar to C. mediale but with spirals more or less obsolete 



especially on the shoulder. 



Lower Lorraine of the Cincinnati dome region. 



LXIV. Trochonema Salter. 

 Turbinate shells with angulated whorls and a wide peripheral 

 band bounded by more or less sharply-defined carinae. Addi- 

 tional carinas at suture and umbilicus often present. Aperture 

 oblique and umbilicus wide. Ordovicic-Siluric. 



Fig. 926. a, b, Trochonema umbilicatum ; c, d, T. umbilicatutn var. (After Ulrich 

 and Scofield, Pal. Minn. ) 



201. T. umbilicatum Hall. (Fig. 926.) Ordovicic. 



Shoulder flat or slightly concave ; peripheral band vertical, 



rarely concave ; umbilicus bounded by well-marked angulation, 



