650 



MOLLUSCA 



PHYLUM VI 



/tw^i/ 



Subfamily H. Cochloceratinae Hyatt. 



Turriliticones with costae similar to those of the preceding group, but more or less 



asymmetrical in consequence of the asymmetry 

 ^/aA of the sjiires. Lobes reduced to four in number, 



and there are other phylogerontic supj^ressions. 

 Funnels monochoanitic, collars absent. 



Gochloccras Hauer (Fig. 1244) ; Paracochloceras 

 Mojs. Trias. 



Family 19. Phylloceratidae Zittel. 



Fig. 1243. 



Rhahdoceras suessi 

 Hauer. Keuper ; 

 Sand ling, near 

 Aussee (after 

 Hauer). 



Fig. 1244. 



Cochlocera s fisch e r i 

 Hauer. Sandling, 

 near Aussee (after 

 Hauor). 



Shells smooth, with radial striae or weak folds. 

 Form compressed, with rounded venters. Body 

 chamber taking up one-half to threefourths of the 

 last volution. Aperture sim])le, with short ventral 

 crest. Lobes and saddles numerous, decreasinfj in 

 size towards the umbilicus. In primitive genera the 

 saddles have monophyllic bases resembling those of the Popanoceratinae, but in the more 

 specialised groups only the marginal saddles retain the rounded outline, the others 

 becoming deeply divided, although always remaining phylloid in termination. 



Monophyllites is the oldest and most primitive of the Phylloceratidae, and 



MonophylUks xlmoiiyi (Hauer). Ujipor Trias ; 

 liothelstein, near Aussee, Austria. 



Fig. 1246. 



Monophyllites billingsianus Gahb. 

 Middle Trias ; Nevada (after Hyatt 

 and Smith). 



probably connects the family with Nomismoceras or some other derivative of the 

 Gephyroceratidae. The resemblance of Phylloceras to the Permian Arcestidae is 

 purely one of convergence, for neither the young of Phylloceras nor the adults of 

 Monophyllites resemble any genera of the Arcestidae. But the young of Phylloceras are 

 like adult Mono'phyUites, and the young of Discophyllites are at first like Nomismoceras, 

 and the adolescent stages like Monophyllites. The development of Monophyllites 

 itself has not yet been studied. 



