CLASS V 



CEPHALOPODA 



661 



Family 24. Haploceratidae Zittel. 



Shell smooth, with fine fjrowth lines, ivühout constrictions. Venter rounded, vnthout 

 Jceel. Apertures with lateral ears or lappets. Septa deeply digitale. 



This family is supposed to be an off-shoot from the Harpoceratidae, and nearly 

 related to Oppelia. 



Haploceras Zittel 

 (Lissoceras Bayle) (Fig. 

 1278). From Middle Jura 

 to Lower Cretaceous. 



Family 25. Stephano- 

 ceratidae Neiimayr. 



Forms usually robust 

 and inclined to be coronate, 

 at least in youth. Surface 

 with bifurcating ribs that 

 extend across the rounded 

 venter. Aperture with 

 lateral ears or lappets^ 

 and usually constricted. 

 Septa deeply digitate, with 

 tivo lateral lobes and two 

 or three auxiliaries. Keel 

 present in some genera. 



The Stephanocera- 

 tidae were derived from the 



Fi(i. 127!t. 



.1, Coelm-eran suharinalum (Youiig). 

 Whitby, Yorkshir«. B, Suture-liiie of 

 Coeloceras pettos Quenst. Middle Lias. 



Fig. 1278. 

 Haploceras eUmatum (Oppel). Tithonian ; Strainberg, Moravia. 



Aegoceratidae of the Lias, and in turn gave rise to 

 most of the Ammonite families of the later Jurassic 

 and Cretaceous, so much so that it might be well to 

 include these and their descendants in a superfamily, 

 or suborder Stephanoceratoidea. 



The group has been subdivided into numerous so- 

 called families, most of which, in so far as they are 

 deserving of recognition at all, are here treated as 

 subfamilies, for the sake of uniformity in Classifica- 

 tion. It is not meant to imply by this that they 

 all have equal taxonomic rank. 



Subfamily A. Dactylioceratinae Hyatt. 



Discoidal forms with costae bifurcated and always 

 Crossing the venter. Sutures with very complex 

 outlines, but only three or four pairs of lateral lobes 

 and saddles. Dorsal sutures have two pairs of saddles 

 and one pair of zygous lobes, 



This series is usually termed the Plaiiulati of the 

 Lias, but althoiigh an ofFslioot of the sarae common stock, 

 it is quite distinct from its supjiosed congeners of the 

 Middle and Upper Jura. Sutures are straight, not in- 

 clined apicad as in Perisphiuctinae. The subfamily com- 

 prises a complete cycle of forms varying from the broad 

 trapezoidal, tuberciilated volutions of Coeloceras through 

 Ariuatoid species to Dactylioceras, in which the costae 

 are smooth and sometimes even single. 



