CEPHALOPODA— AMMONOIDEA. 1 89 



324. A. 'avellanoides Uhlig. Jurassic. 

 Small, subglobular; whorls broad, strongly embracing; umbilicus 



rather small, but deep ; a row of small, crowded tubercles at umbil- 

 ical margin, absent from outer margin; feeble undulations and 

 irregular striations characterize the shell surface. 



Kimeridgian of Sierra de Santa Rosa, Mexico ; Spiti shales of 

 Himalayas. 



325. A. alamitocense Castillo and Aguilera. Jurassic. 

 Very large, the ribs obsolete or represented by faint wrinkles, 



outer row of tubercles about the middle of the body whorl. 



Tithonian of San Luis Potosi, Mexico; Malone formation of 

 Texas. 



MORPHOCERATIDA. 



CXLIII. Olcostephanus Neumayr. 



Differs from Perisphinctes in the higher whorls, and generally 

 smaller umbilicus, ribs dividing near umbilical angulation and con- 

 tinuing as bundles across the rounded venter; they mostly lack 

 the regularity and precision of those of Perisphinctes; suture 

 strongly incised. Upper Jurassic^Cretacic. 



326. 0. (Simbirskites) mutabilis Stanton. (Fig. 1447.) Comanchic. 



Fig. 1447. Olcostephanus {Simbirskites) mutabilis, X %> '^^^^ suture. (After 

 Stanton. ) 



Comparatively small, with small umbilicus and much compressed 

 whorls ; costse numerous, but irregular, generally dividing into two 

 to four, rarely five branches at about the middle of the side, and 

 curving forward at the venter. 



Knoxville of California. 



