CEPHALOPODA— AMMONOIDEA. 



185 



CXXXIX. Cardioceras Neumayr and Uhlig. 



Involute ammonites with angular venter and more or less tri- 

 angular section, and moderate but deep umbilicus ; a strong ventral 

 keel corded by fine, multiple ribs, and more or less prominent, 

 frequently bifurcating sigmoid ribs characterize the surface; 

 suture with broad lobes and saddles, much incised ; the siphonal 

 saddle broad, the antisiphonal lobe singly pointed. Jurassic. 



312. C. cordiformis M. and H. (Fig. 1442.) Jurassic. 



Fig. 1442. Cardioceras cordiformis, 'y^%, st^XwTa Qr\\2irgtd. (After Whitfield, 

 Pal.Blk. Hills.) 



Ventricose, with sides nearly flat and umbilical shoulder abrupt, 

 less than 90° ; ribs divide near umbilicus and again into numerous 

 divisions near keel. 



Upper Jurassic of Black Hills. 



CXL. Perisphinctes Waagen. 



Discoidal, scarcely involute, and widely umbilicated ammonites 

 with rounded venter and mostly flattened sides ; ribs strong, bifur- 

 cating and tri furcating near venter, which they cross uninterrupt- 

 edly; intercalations may replace the bifurcations; suture finely 

 incised; siphonal and first lateral lobe large; second lateral lobe 

 small; inner parts of suture steeply incHned apicad, with a long 



