DISCOCEKAS, r,()!{.()NICKIt,.\S, ASTEHOCKRAS. 227 



defined U[)on the second whorl. Umbilicus open ; sides exposed. 

 Abdominal lobe deeper and narrower than the lateral lobes. 

 Superior lateral lobes broad, shallow, and but very little longer 

 than the inferior lateral. The auxiliary lateral lobes are cunei- 

 form, and incline towards the umbilicus. 



Lower and Upper Lias. 



0. TORUS, d'Orb. T. 107, figs. G12, 613. 



DiscocERAS. Abdomen keeled and channeled. Both charac. 

 ters are constant, although the channels are sometimes nearly 

 obsolete. Pilce smooth. Geniculse curved forwards. Umbili- 

 cus open, sides flattened, exposed. Abdomen depressed. Ab- 

 dominal lobe deep and narrow. Superior and inferior lateral, 

 narrow and irregularly pointed with minor lobes. Superior 

 lateral cell equally divided. Inferior lateral unequally divided. 

 First auxiliary cell well developed, and nearly as long as the in- 

 ferior lateral. 



Lower Lias. 



D. oPHiDioiDES, d'Orb. T. 107, figs. 607, 608. 



CoRONiCERAS. Kccls prominent, constant ; channels well 

 defined. Pilae tuberculated and bent. Umbilicus open. Sides 

 of the whorls exposed. Pilee preceded by a line of tubercles in 

 the young, which gradually elongate to form the tuberculated 

 pilae of the adult. Yenti'al lobe deep and narrow. Lateral lobes 

 unequally divided. Superior lateral cell irregularly divided ; 

 abrupt on the siphonal side ; sloping rapidly on the opposite 

 side. Inferior lateral cell exceedingly variable in form, but un- 

 equally divided. 



Lower Lias. 



C. BisuLCATUs, d'Orb. T. 103, fig. 557. 



AsTEROCERAS. Keel well defined, but varies from prominent 

 and narrow to depressed and broad. Channels obscure to deep 

 and well defined. Pila? smooth, depressed ; often bent on the 

 sides, and appear in the young as lateral folds or large tubercles. 

 Sides in some species not enveloped ; in others, covered to fully 

 one-half of their breadth. Ventral lobes very deep. Lateral 

 lobes very shallow. Superior and first auxiliary cells short and 

 broad. Inferior lateral cell very prominent. 



Lower Lias. 



A. oBTUSus, Sowb. T. 107, figs. 614, 615. 



