384 INFERIOR OOLITE AMMONITES. 



AN OUTLINE OF THE CLASSIFICATION OF THE CONCAVUM- 



ZONE SONNMIM. 



I. The terminal lobule of L is axial in the spinous stage, and 



generally isosceloid. 



A. The terminal lobule remains axial during phyletic development. 

 A. The lateral lobules of L equipoised, isometric, non-partite. 



Fig. 4. — Outline of L of Sonn. donrinatrix. 



a. Costse strong. 

 Sonninia dominateix. (Page 392.) 



/3. Costa? weak. 

 Sonn. tridacttla. (Page 393.) 



B. The lateral lobules of L isometric, bipartite. 

 \ 



Fig. 5. — Outline of L of Sonn. papilionacea. 



Sonn. spinosa. (Pages 365 and 394.) 

 Sonn. quadrifida. (Pages 366 and 394.) 

 Sonn. papilionacea. (Pages 367 and 394.) 



B. The terminal lobule of L becomes slightly intra-axial. 

 A. Lateral lobules of L short and both bipartite. 



Fig. 6. — Outline of L of Sonn. costata. 



