658 



MOLLUSCA 



PHYLUM VI 



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

 costae. The latter are straiglit in i^rimitive Catulloceras, wliich resenibles Caloceras 



in aspect. Discoidal forms often both 

 keeled and channelled on the venter, and 

 sometimes have broad furrows on the 

 sides. Specialised invohite shells have 

 solid keels, bnt iisually no Channels, and 

 lateral zones often become smootli. Sutures 

 comparatively simple, and in discoidal 

 forms are similar to those of Ärnioceras, 

 biit more complex in highly involute 

 forms, 



Harpoceras Waagen, and subgenera : 

 Hildoceras (Fig. 1268), Lioceras (Fig. 

 1269), Grammoceras Hyatt (Fig. 1270); 

 Gatulloceras Gemm. ; Arietieras Seg. ; 

 Hyperlioceras, Graphoceras, Brasilia and 

 Darellia Buckman. Upper Lias and In- 

 ferior Oolite. 



Poecilomorphus, Huddlestonia^ 

 Brodieia, Gosmogyria, Welschia Buckman ; 

 Ludwigia Bayle, These are also subgenera from the Inferior Oolite. 



Fio. 1270. 



Harpoceras Grammoceras thouarsensi d'Orb. Upper 

 Lias ; Heiningen, Würtemberg. 



Subfamily B. Oppeliinae Hang. 



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

 species that show affinity with Harpoceran stock, and apparent derivation from Poecilo- 

 morphus 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 become very prominent, and fiUed with shell layers, 

 but never hoUow. It disappears on the body Chamber. 

 Aperture with ventral crest. The sigmoidal ribs often end 

 in marginal knots. Septa finely digitate. This subfamily 

 ranges from the Middle Jura to the Cretaceous, its maximum 

 falling 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). p^^, ^271. 



Oppelia has been subdivided into a large number of oecotraustes macrotelns 

 groups, or transitional series (" Formenreihe "), some of which (^ppei). Tithonian ; stram- 

 might 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, but 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 unornamented shells. Aperture sometimes 

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

 ceratidae. 



Gadomoceras, Creiiiceras, Mun.-Chalm. (Fig. 1272); Phlycticeras 

 {Lophoceras Bonar.) ; Ochetoceras Hang (Fig. 1273); Gy macer as 

 Quenst. (emend. Hyatt). Type G. (Ammonites) guemheli (Opp.). Strigoceras Quenst. 



Fig. 1272. 

 Creniceraa renggcri 

 (Oppel). Oxford i an ; 

 Salins, Jura. 



