92 BULLETIN OF THE 



Platypleuroceras * Hyatt. 

 Abdomen nearly as broad, or broader, than the dorsal side of the whorl. 

 Pila; single, tuberculated, and extending across the rounded abdomen, as in 

 Planiceras. The septa are minutely divided by minor lobes, very closely 

 set. The abdominal lobe is deep ; sides abrupt. Superior lateral very 

 narrow, deeper than the abdominal, and profusely brandling. Inferior 

 lateral not as deep as superior lateral, and of about the same breadth and 

 general aspect. Abdominal cell large and serrated. Superior lateral very 

 broad, about the same height as the inferior lateral. 



Platypleuroceras latsecosta Hyatt. 



Amm. latcecosla Sow., Min. Conch., v. G, p. 10G, pi. 556. 

 Amm. lakecosta Ziet., Verst. Wiirt., p. 3G, pi. 27, fig. 3. 

 Amm. natrix-rolundus Quens'dt, Die Ceph., p. 85, pi. 4, fig. 17. 

 Loc. Gegenberg, Hinterweiler, Welflingcn, Kentlingen, and Balingen ; 

 Coll. Mus. of Stuttgart, L. Agassiz, Ur. Krantz, and L. de Koninck. 



Cyclocerast Hyatt. 

 Abdomen rounded or keeled, not so broad as the dorsal side of the whorl. 

 Pilse single, tuberculated, and not extending across the abdomen in the 

 keeled species. Young smooth for the first two or three whorls, then be- 

 come ribbed. Keel appears at an earlier stage of growth than the pila?. 

 Septa not so minutely divided by minor lobes, and the large lobes less 

 dendritic than in Platypleuroceras. The abdominal lobe of medium depth, 

 and quite broad. Superior lateral of medium breadth and considerable 

 depth. Inferior lateral about two thirds as broad and deep as superior 

 lateral. One small auxiliary lobe exposed laterally. Superior lateral cell 

 broad and depressed. Inferior lateral more prominent and narrower ; 

 small auxiliary cell exposed on the side. 



Cycloceras molare Hyatt. 



Amm. natrix oblongus Quens'dt, Die Ceph., p. 85, pi. 4, fig. 16. 

 Loc. Balingen ; Coll. L. de Koninck. 



Cycloceras natrix Hyatt. 



Amm. natrix Schlot., Petrefaktenkunde. 



Amm. natrix Ziet., Verst. Wiirt., p. 5, pi. 4, fig. 5. 



Loc. Balingen and Rentlingen ; Coll. L. de Koninck and Dr. Krantz. 



Cycloceras Valdani Hyatt. 



Amm. Valdani D'Orb., Terr. Jurass., Ceph., p. 255, pi. 71. 

 Amm. compressus Quens'dt, Die Ceph., p. 90, pi. 5. fig. 3. 



* ItXarvs, flat, and H\tvpoi>, rib. | Kv*Aor, circle. 



