656 



MOLLUSCA 



PHYLUM VI 



and resembles (as do also the two dorsal saddles and small dorsal lobes) tliose of 

 tlie Arietitinae. 



7..S-1 7.,S'" '"' !■ 



IL 



Fior 1265. 



Arütites Hsulcatus Brug. Lower Lias ; Würtemburg. A, Suture line ; B, (\ Portion of volution seen froiu 



the lateral and ventral aspects. 



Äegoceras Waagen (Fig. 1266) 

 Hyatt has proposed tlie following 

 snbgenera : Liparoceras, Microdero- 

 ceras and Ändrogynoceras. Lower and 

 Middle Lias. 



The second group is tliat of Schlo- 

 theimia Bayle, called by Hyatt the 

 " Angulatidae." This includes more 

 or less compressed and costated shells, 

 the costae sometimes crossing the 

 venter in the young or extreme age, 

 but usually interrupted in the adult 

 by a smooth and occasionally sunken 

 median zone. Sutures inclined apicad 

 near lines of involution, more com- 

 plex in outline than in typical Ärie- 

 tites, and with phylliform marginals 

 Ventral lobe broader and shorter, with larger siphonal 



Fig. 1266. 



•ö mpricornus (Schloth.). Middle Lias 

 Gmünd, Würteniberg. 



more like tliose of Psilocen 



