670 MOLLUSCA SUB-KINGDOM vr 



Family 5. Distichioceratidae. Sutures simpler than in Glochiceratidae, owing 



Fio. 1180. 



Ochetoceras flexuosum, v. Buch p. Upper 

 Jura (/3) ; Laufen, Wiirtemberg. 



Strellites tenuilobatus, Oppel sp. Upper 

 Jura ; Pappenheim, Bavaria. 



to arrested development. Young of Distichioceras 

 repeat the characteristic form and costae of the latter, 

 with smooth venter and lateral tubercles, and then 

 acquire the features of Horioceras before the median 

 continuous keel of Distichioceras arises. 



Includes Horioceras and Distichioceras, Mimier- 

 Chalmas. Jura. 



Family 6. Silesitidae. Similar to Haplocera- 

 tidae, but costae more strongly developed, and some- 

 times spinous. 



Silesites, Holcodiscus, Uhlig ; Pachydiscus, Zittel 

 (Figs. 1182, 1183); Parapachydiscus, gen. nov. Type 

 P. (Amm.) gollevillensis, d'Orb. sp. ; Pseudohaploceras, 



Fio. 1182. 

 Patfiydiscus jyer.amphis, Mantell sp. Lower Chalk ; England. 



FIG. 1183. 



Pachydisais Wittekindi, Schliiter sp. 

 Upper Cretaceous ; Haldem, West- 

 phalia. 1/3- 



gen. nov. Type P. (Hapl.) liptoviense, Uhlig sp. ; GabUoceras, gen. nov. Type G. 



