570 MOLLUSCGA 
SUB-KINGDOM VI 
Family 5. Distichioceratidae. Sutures simpler than in Glochiceratidae, owing 

Fic. 1180. 
Ochetoceras flecuosum, v. Buch sp. Upper 
Jura (8); Laufen, Wiirtemberg. 
to arrested development. Young of Dz¢stichioceras 
repeat the characteristic form and costae of the latter, 
with smooth venter and lateral tubercles, and then 
acquire the features of Horioceras hefore the median 
continuous keel of Distichioceras arises. 
Includes Horioceras and Distichioceras, Munier- 
Chalmas. Jura. 
Family 6. Silesitidae. Similar to Huaplocera- 
tidae, but costae more strongly developed, and some- 
times spinous. 
Silesites, Holcodiscus, Uhlig; Pachydiscus, Zittel 
(Figs. 1182, 1183); Parapachydiscus, gen. nov. Type 
P. (Ami.) gollevillensis, V@Orb. sp.; Pseudohaploceras, 

Fic. 1182. 
Pachydiscus poramp'us, Mantell sp. Lower Chalk; England. 
fo] 
Upper 
phalia. 
Fic. 1181. 
Streblites tenuilobatus, Oppel sp. Upper 
Jura; Pappenheim, Bavaria. 
ae Se 


Fic. 1183. 
Pachydiscus Wittekindi, Schliiter sp. 
Cretaceous ; 
1/g, 
Haldem, West- 
gen. noy. Type P. (Hapl.) liptoviense, Uhlig sp.; Gabbioceras, gen. nov. Type G. 
- a 
ia A i a ‘is », 
ee 
—— 
