CLASS V 



CEPHALOPODA 



661 



Fig. 1278. 

 Haploceras elimaUim (Oppel). Tithonian ; Stramberg, Moravia. 



Family 24. Haploceratidae Zittel. 



Shell smooth, tvifh fine groivth lines, ivithout const notions. Venter rounded, ivithout 

 keel. Apertures with lateral ears or lap2)ets. Septa deeply digitate. 



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 J ura 

 to Lower Cretaceous. 



Family 25. Stephano- 

 ceratidae Neumayr. 



Forms usually robust 



and inclined to he coronate, 



at least in youth. Surface 



tvith bifurcating ribs that 



extend across the rounded 



venter. Aperture ivith 



lateral ears or lappets, 



and usually constricted. 



Septa deeply digitate, tvith 



two lateral lobes and two, 



or three auxiliaries. Keel 



present in some genera. 

 The Stejihanocera- 



tidae were derived from the 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 Ijifurcated 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 Planulati of the 

 Lias, but although an offshoot of the same common stock, 

 it is quite distinct from its supposed congeners of the 

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

 clined apicad as in Perispliiuctinae. The subfamily com- 

 prises a complete cycle of forms varying from the broad 

 A, Coelocera, suharm.UuM (Young), ti-apezoidal, tuberculated volutions of Coeloceras through 

 Whitby, Yorkshire. B, Suture-line of Armatoid species to Dactyhoccras, 111 wiucli the costae 

 Coeloceras pettos (^uenst. Middle Lias. are smooth and sometimes even single. 



jB 



Fig. 127!>. 



