CLASS V 



CEPHALOPODA 



659 



(Buckman) ; Streblites Hyatt (Fig. 1274). Type S. {Ammonites) pictus-costatus 

 (Quenst). Glochiceras Hyatt. Middle and Ui)per Jura. 



Another group, which Hyatt called " Distichioceratidae," includes the genera 



Fig. 1273. 



Ochetoccras flexiwsum (v. Buch). Upper 

 Jura (j3) ; Laufen, Wiirtemberg. 



Fig. 1274. 



StrchlUes tenuilohatus (Oppel). Upper Jura ; 

 Pappenheim, Bavaria. 



Horioceras and Distichoceras Munier-Chalmas, with septa simpler than in Glochiceras, 

 owing to arrested develoiyment. The young of Distichoceras repeat the characteristic 

 form and costae of Glochiceras, with smooth venter and lateral tubercles, and then 

 acquire the features of Horioceras before the 

 median continuous keel of Distichoceras arises. 



Family 23. Amaltheidae Fischer (pars). 



Form laterally compressed, usually involute, 

 high whorled. Sides with gently curved ribs or 

 folds, and often with lateral knots or spiral 

 lines. Venter keeled, and the keel is often 

 crenulated by ribs or thickened growth lines. 

 Aperture simple, or with narrow ventral crest. 

 Sutures deeply digitate with several auxiliary 

 lobes. 



Subfamily A. Amaltheinae Hyatt. 



Discoidal and involute shells, the young of 

 which have fold -like costae rising into heavy 

 nodes just inside the lines of involution. Costae 

 became prominent and sharp at the umbilical ^/maWmis margariwm Montf Middle 



.j.^v^u,iiiv- |_j.v^ ii ^ Lias; Wurtemberg. Living chamber broken 



shoulders and ventro- lateral angles, and true away and exposing " wrinkled layer " on 

 ,11 • „ „,.^,-,,^c "VronfoT. l-colorl ventral surface. This is homologous with the 



tubercles appear m some groups. Venter keeled «biack layer" of iVaufHus. 



and sulcated in discoidal forms, the keels alone 



persisting in more involute species. Keel solid and crenulated by the passage of costae 



or folds across the venter. Anaptychus present. Nodes prominent in the young of 



primitive species ; costae with only one row of tubercles in later stages or none ; keel 



invariably present and crenulated. Amaltheus Montf. (Figs. 1 150 ; 1160, ^ ; 1275) ; 



Paltopleuroceras Buckm. {Pleuroceras Hyatt). Middle Lias. 



Fio. 1275. 



