646 



MOLLUSCA 



PHYLUM VI 



Family 17. Hungaritidae Diener. 

 Form involute, laterally compressed, with keeled venter. Surface often ornamented 



Idaho 1/2 (after Hyatt and Smith), 



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Fig. 1232. 



Inyoites oweni H. and S. Lower Trias ; California 

 (after Hyatt and Smith). 



with folds, rihs or hnots. Body 

 Chamber short. Septa usually cera- 

 titic, not reaching the digitate stage 

 in any genera, hut persisting in the 

 goniatitic stage in Beneckeia. 



This group is not regarded as 

 a side branch from the Meekoce- 

 ratidae, but as an old and persistent 

 stock, Coming down with little modification from the Gephyroceratidae, probably 

 from the keeled form Timanites. The Hungaritidae have been confused with the 

 group of keeled Geratites, and also with compressed members of the Tropitidae, but 

 the resemblance is one of convergence, and bespeaks no near relationship. 



Hungarites Mojs. ; Otoceras Griesbach. Permian and Trias. Beneckeia Mojs. ; 

 Inyoites Hyatt and Smith (Fig. 1232); Dalmatites Kittl. Permian and Trias. 

 Eutomoceras Hyatt {Halilucites Diener). Trias. 



Family 18. Ceratitidae Mojsisovics. 



Forms evolute to involute^ laterally compressed to robust and rounded. Surface 

 usually ornamented with folds, ribs, knots, spines or tubercles. Venter in some genera 

 provided with a keel, in others with a median furrow ; and occasionally biangidar. Body 

 Chamber rather short. Septa ranging from the goniatitic stage in some arrested or re- 

 versionary forms, through the typical ceratitic stage, to complex digitation. 



This family may be, and probably is, polyphyletic, but a large part of it, including 

 the typical Geratites, seems to have been derived from Meekoceras or from some member 

 of that group. Only the more primitive members of Geratites show a youthful stage 

 similar to Meekoceras, but there seems to be a perfect intergradation between the more 

 complex species of Meekoceras and the more primitive species of Geratites. 



Subfamily A. Ceratitinae Mojsisovics. 



Primitive forms are discoidal or involute, but stout-whorled and keelless, becoming 

 more compressed, and having a broad, slightly elevated median ventral ridge in more 

 specialised genera. Sides have at least one line of nodes in primitive forms, and are more 



