650 



MOLLUSCA 



PHYLUM VI 



/iW^K 



Siibfamily H. Cochloceratinae Hyatt. 



Turriliticones vvith costae similar to those of the preceding groiip, but more or less 



asymmetrical in conseqiience of the asymmetry 

 of the spires. Lobes reduced to foiir in niimber, 

 and there are other phylogerontic suppressions, 

 Funnels monochoanitic, collars absent. 



Gochloceras Hauer (Fig. 1244) ; Paracochloceras 

 Mojs. Trias. 



Family 19. Phylloceratidae Zittel. 



Fig. 1243. 



RhaJ)doceras suessi 

 Hauer. Keuper ; 

 Sandling, near 

 Aussee (after 

 Hauer). 



Shells smooth, wiih radial Striae or weak folds. 

 Form compressed, with rounded venters. Body 

 ,, " , - ,,. Chamber tahing up one-half to three-fourths of the 



Hauer. Sandling, last volution. Aperture simple, with short ventral 

 Hauer)."^'"'^^ ^^ crest. Lohes and saddles numerous, decreasing in 

 size towards the umhilicus. In primitive genera the 

 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 



fffP 



V^-; 



Fic. 1:^45. 



Mouüphyliitcs dmonyi (Hauer). Upper Trias 



Rötheistein, near Aussee, Austria. 



Fig. 1246. 



Monophyllites hillingsicmns Gabb. 

 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 adiilts of 

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

 like adult Monophyllites, and the young of Discophyllites are at first like Nomismoceras, 

 and the adolescent stages like Monophyllites. The developnient of Monophyllites 

 itself has not yet been studied. 



