23fi ErDJSCnCKUAS, COKOCEKAS. KTC. 



Genus EUDISCOCERAS, Hyatt. 



This type is distinguished by its discoid form, open umbilicus, 

 and mi abdominal keel, bordered by furrows and ridges, the 

 latter being interrupted or tubercular ; the young with compar- 

 atively large pihv, growing smaller and more flcxuous in the 

 adult, and finally fading away in the larger half of the body- 

 volution. 



E. GABBI, Meek. PL 10r>, iigs. ,V,>7, 51)8. Trias. 



Family CLYDON1T1D.K. Hyatt. (Includes Glij<ln,t.Ht>.*. Hauer, 

 and Corocera*, Hyatt.) 



COROCERAS, Hyatt. The species all have numerous lobes and 

 cells, with smooth sutures, and a large abdominal lobe; the 

 latter being very broad and proniinenl . They are pileately ribbed 

 and very involute ; the umbilicus nearly covered. The mouth 

 is more or less hooded or constricted. 



C. ELLIPTIC! s. Hauer. T. KM;, figs. f>',) ( .. r>(H). Triassic. Hall- 

 stott. 



Professor Hyatt remarks that the species included in Cli/do- 

 nile* form a heterogeneous assemblage of diverse types from 

 which it will be necessary to eliminate other new generic groups. 



Family AKIKTID.K. 



Genus AOASSICERAS, Hyatt. Voting quite immature and re- 

 markable for the prolonged existence of the goniatitic form 

 which is generally confined to the earliest stage of growth in the 

 Ammonites. The living chambers are <j',iite short, the abdomen 

 keeled, but not channeled. This genus would not be placed in 

 the group of Arietid;e by many auihors. A comparison of the 

 adult with the perfect young of A. ohfnxtis shows, however, that 

 botli have similar forms and short living chambers. 



A<;.\ssi<'KK.\s SCIPIONIAM s, d'Orb. T. 10<S. Iigs. i;^'.);'63U. 



Family OX YNOTID.J']. Young similar to the group of certain 

 aberrant forms of Arietidse, but the adult instead of the 

 solid keel of A rietida- possesses a hollow keel. In the old, 

 however, this keel entirely disappears, leaving the abdomen 

 rounded and almost flattened, a t ransformation entirely dis- 



