236 EUDISCOCERAS, roROCERAS. ETC. 



Genus ETJDISCOCERAS, Hyatt. 



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

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

 latter being interrupted or tubercular ; the young with compar- 

 atively large pila*, growing smaller and more flexuous in the 

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

 volution. 



E. Gabbi, Meek. PI. IOC, tiys. .^97, 5i)8. Trias. Nevada. 



Family CLYDONITID^, Hyatt. (Includes Glydonites, Hauer, 

 and Cor-oceras, 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 prominent. They are pileately ribbed 

 and very involute ; the umbilicus nearly covered. The mouth 

 is more or less hooded or constricted. 



C. ELLiPTH'US. Hauer. T. 10<;, tigs. r)il«l, COO. Triassic. Mall- 

 ><tatt. 



Professor Hyatt remarks that the species included in Glydo- 

 iiUes form a heterogeneous assemblage of diverse types from 

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



Family ARIETIH^E. 



Genus Agassiceras, Hyatt. Young quite immature and re- 

 markable for the prolonged existence of the goniatitic form 

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

 Ammonites. The living chambers are quite short, the abdomen 

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

 the group of Arietidje by many authors. A comparison of the 

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

 both have similar forms and short living chambers. 



Agassiceras Scipionianus, d'Orb. T. 108, figs. (*>-2i), 630. 



Family OXYXOTID^E. Young similar to the group of certain 

 aberrant forms of Arietidie, but the adult instead of the 

 solid keel of Arietidse possesses a hollow keel. In the old, 

 however, this keel entirely disapi)ears, leaving the abdomen 

 rounded and almost flattened, a transformation entirely dis- 



