390 



INFERIOR OOLITE AMMONITES. 



a. Costae weak. 

 Sonn. spinifera. (Pages 335 and 418.) 



/3. Costae strong. 



Sonn. acanthodes. (Pages 319 and 419.) 

 Sonn. ptyota. (Pages 332 and 420.) 

 Sonn. oymatera. (Pages 332 and 420.) 



G. The lobes remain long, but L becomes very asymmetrical, 

 a. Inner lobule of L much abbreviated in spinous species. 



Fig. 22. — Outline of L of Sonn. gibbera. 



Fig. 23. — Outline of L of Sonn. modesta. 



1. Costse regular. 



Sonn. reclinans. (Page 421.) 

 Sonn. gibbera. (Page 421.) 

 Sonn. modesta. (Pages 325 and 422.) 

 Sonn. simplex. (Pages 326 and 423.) 



2. Costse faired. 



Sonn. alternata. (Pages 346 and 424.) 



/3. Inner lobule of L not abbreviated in spinous species (but it is so later on in the phyletic series). 



Fig. 24. — Outline of L of Sonn. subirregularis. 



Fig. 25. — Outline of L of Sonn. subsimplex. 



Sonn. multispinata. (Pages 317 and 425.) 

 Sonn. crassispinata. (Pages 317 and 425.) 

 Sonn. subirregularis. (Page 426.) 

 Sonn. subsimplex. (Pages 328 and 427.) 



