CLASS V 



CEPHALOPODA 



659 



(Buckman); StrehUtes Hyatt (Fig. 1274). Type S. (Ämmonites) iiidus-costatus 

 (Quenst.). Glochiceras Hyatt. Middle and Upper Jura. 



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



1273. 



Ochetoceras flexuosum (v. Buch). Upper 

 Jura (jS) ; Laufen, Würtemberg. 



Fig. 1274. 



StreUites tenuilöbatus (Oppel). Upper Jura 



Pappenheim, Bavaria. 



Horioceras and Distichoceras Munier-Chalmas, witli septa simpler than in GlochiceraS) 

 owing to arrested development. The yoimg of Distichoceras repeat the characteristic 

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

 acqiiire the featiires of Horioceras before the 

 median continuoiis keel of Distichoceras arises. 



Family 23. Amaltheidae Fischer (pars). 



Form laterally compressed, usnally 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. Amaltheinäe 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 



Pio. 127 



AmaWieus margaritatus Montf. Middle 

 ■Uli 1 j. 1 i. 1 1 j 4. ^'*^ ' Würtemberg. Living Chamber broken 



Shoulders and ventro- lateral angles, and true away and exposing " wrinkied layer " on 

 tubercles appear in some groups. Venter keeled IT^^^} f"^^^?,"-, V^^^Jl^ homoiogous witii the 



T 11 , 11^ Till olack layer of Nautilus. 



and sulcated m 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. 



