84 AMMONITID^. 



the lobes. First lateral always longer than the siphonal lobe ; 

 second lateral strikingly short ; auxiliary horizontal or very 

 slightly depending. 



Olcostephanus, Neumayr, 18T5. 



Distr. — 33 sp. Jurassic to Cretaceous ; Europe, India. O.Bha- 

 wani, Stol. (xl, 53, 54). 



Body-chamber only about one-third of the last whorl ; surface 

 ornamented by ribs which are interrupted at the rounded per- 

 iphery ; aperture simple or eared, contracted ; most of the species 

 are distantly constricted ; sutural line complicated by the pres- 

 ence of three auxiliary lobes. 



b. U volute. 



SoAPHiTES, Parkinson, 1811. 



Etyra. — Scaphe, a boat. 



Distr.— Si sp. Cretaceous; Europe, America. S. sequalis, 

 Sowb. (xxxii, 35). Sussex, England. 



Shell at first closely spiral, involute, at length detached and 

 recurved ; sutures many-lobed, lobes foliated. 



The Scaphites (with the exclusion of Sc. Yvanii) form a very 

 good natural group, very distinctly characterized by the involute 

 spiral of the chambered portion of the tube, to which but one 

 ver}^ short evolute hook is attached, by their aptychus, which by 

 its form, its want of strong longitudinal sculpture, and the sur- 

 face covered with granules, is allied to the aptj'^chi of Peri- 

 sphinctes, and by the appearance of auxiliary lobes, which are 

 wanting in all other evolute forms. The form of the aptychus 

 decidedly indicates that they are serially to be connected with 

 the Perisphinctes-stem, and the form of the inner whorls of the 

 geologically old species, which agree entirely in form with Olc. 

 Guastaldinus, indicates strongly their connection with Olcoste- 

 phanus, which is also confirmed by the form of the aperture. 



DiscosoAPHiTES, Meek, 1816. For forms, the ornamentation of 

 which recalls that of Acanthoceras. S. Gheyennensis, Owen ; 

 ;S. Gonradij Morton. 



Hamites, Parkinson, 1811. 



-Etym. — Hamus, a hook. Syn. — Ammonoceras, Lam., 1822. 



Distr. — 150 sp. Cretaceous. H. attenuatus, Sowb. (xxxiii,40). 

 H. cylindraceus, Defr. (xxxiii, 41). 



Shell with the tube unrolled, and variable in ornamentation ; 

 sutural line rather simple ; a siphonal lobe, two lateral lobes 

 divided into pairs — sometimes symmetrical, sometimes asym- 

 metrical in the second lobe ; rarely with auxiliary lobes. 

 Aptychus (?). 



Hamites may include all the unwhorled Ammonitas of the 



