658 



MOLLUSCA 



PHYLUM \I 



although prominent crescentic ridges may arise on the sides through confluence of 

 costae. The latter are straiglit in primitive Gatulloceras, which resembles Culoccras 



in aspect. Discoidal forms often both 

 keeled and channelled on the venter, and 

 sometimes have broad furrows on the 

 sides. Specialised involute shells have 

 solid keels, but usually no channels, and 

 lateral zones often become smooth. Sutures 

 comparatively simple, and in discoidal 

 forms are similar to those of Arnioceras, 

 but more complex in highly involute 

 forms. 



Harpoceras Waagen, and subgenera : 

 Hildoceras (Fig. 1268), Lioccrcn^ (Fig. 

 1269), Grammoceras Hyatt (Fig. 1270); 

 Catulloceras Gemm. ; Aridieras Seg. ; 

 Hyperlioccras, Graphoceras, Brasilia and 

 Darellia Buckiuan. Upper Lias and In- 

 ferior Oolite. 



Poecilomo rp h u s, Hu (Idle .s- 1 o n i «, 

 Brodieia, Gosmogyria, JVelschia Buckman ; 

 These are also subgenera from the Inferior Oolite. 



Fio. 1270. 



Ilarpoceras Grammoceras thouarsensi d'Orb. 

 Lias ; Heiningen, Wiirtemberg. 



Upper 



Ludwiyia Bayle. 



Subfamily B. Oppeliinae Hang. 



Discoidal and highly involute shells with sutures, form and markings in primitive 

 species that show affinity with Harpoceran stock, and aj)parent derivation from Poecilo- 



morplius through typical Oecotraustes. Costae highly flexed and sometimes fused, but 



no well-marked lateral channels as in hollow-keeled groups. Venter often truncated 



and sides flattened, except in primitive species. The keel 



may Ijecome very prominent, and filled with shell layers, 



but never hollow. It disappears on the body chamber. 



Aperture with ventral crest. The sigmoidal ribs often end 



in marginal knots. Septa finely digitate. This subfamily 



rano-es from the Middle Jura to the Cretaceous, its maximinn 



fallinfT in the Upper Jura. Typical genera are Oppelia 



Waagen (Figs. 1155, 1157, and 1158), and Oecotraustes 



Waagen (Fig. 1271). A revision of the group has recently 



been published by Douville (1913). 



Oppelia has been subdivided into a large number of 



groups, or transitional series (" Formenreihe "), some of which |3^}.'|^J^OTav 



mi<dit even take rank as subfamilies, but most of them 



are'' hardly more than subgenera. The largest group, which Hyatt distinguished 

 under the name " Glochiceratidae," includes discoidal and involute 

 shells, smooth in primitive species, Imt acquiring highly inflected 

 costations, sometimes with two rows of tubercles on the sides, and 

 a median ventral row that may fuse into a continuous solid keel. 

 One line of ventral tubercles may also arise directly from folds that 

 appear in otherwise unornameuted shells. Ajterture sometimes 

 with long lateral lappets. Sutures similar to those in the Haplo- 

 ceratidae. 



Gadoinoccras, Grmiceras, Mun.-Chalm. (Fig. 1272); Phhjcticcras 

 {Lophoceras Bonar.) ; Ochetoceras Hang (Fig. 1273); Gymaceras 



Quenst. (emend. Hyatt). Type C. {Ammonites) guembeli (0pp.). Strigoceras Quenst. 



Fig. 1271. 



Oecotranntes macrotelvs 

 Titlionian ; Stram- 

 ia. 



Kio. 1272. 

 Crcnireras rewigeri 

 (Oppfil). Oxfonlian ; 

 Saliiis, Jura. 



