THE CEPHALOPODA. 



191 



in a complete half circle ; and the sides fall off towards the suture, which have often a 

 sharper border, and sometimes a perpendicular surface. 



Fig. 64. — Stephanoceras coronatum, Brug. Fig. 65. — Steph. coronatum, Brug. Fig. &6.—Slephanoceras tumidum, Ziet. 

 Side view. Front view. Front view. 



The lower lateral stands always above the inner border, not under it, as in the Coro- 

 NARii. The very large ventral lobe is accompanied by two extended arms, and besides 

 by two auxiliary lobes. The upper lateral stands always directly opposite the arms of the 

 columellar, the under lateral directly opposite the lower auxiliary. 



Stephanoceras coronatum, Brugiere (fig. 64). I Stephanoceras macrocephalum, Schloth. 



— modiolare, Lhwyd. \ — tumidum, Zieten (fig. 66). 



IX. Armati.— Two or more rows of tubercles form a longitudinal parallel series upon 

 the sides, but rarely on the siphonal area, which is flat, often broader 

 than the sides, and joined to them by an almost right-angled border. 

 The upper row of tubercles stand upon the border ; then follows a 

 vacant space between them and the lower series, in which the 

 upper lateral lobe comes in ; then follows either one or more rows 

 of tubercles. The siphonal lobe is somewhat deeper than the upper 

 lateral, which is sometimes almost three times as deep as it is 

 broad. The siphonal saddle is always of a remarkable breadth, 

 more than double that of the upper lateral, with a deep 

 secondary lobe in the middle and quite even above. The 

 lower lateral, on the other hand, is not larger than the secondary lobes of the siphonal 

 saddle. This is a remarkable group, and very rich in species, found chiefly in the 

 uppermost strata of the Oolitic series and the Cretaceous formation. Aegoceras Birchii 

 and Aec/. Henleyi occur in the Middle Lias, and Aspidoceras lonffispinum (fig. 67) in 

 the Oxford clay. Hoplites mammillaris (fig. 69, 70), H. Bhotomagensis, H. Mantelli, and 

 H. Woolffuri represent Cretaceous forms. The following are typical species : 



Fig. 67. — Aspidoceras longi- 

 spinum, Sow. 



Aegoceras Birchii, Sow. 

 Aspidoceras perarraatum, Sow. 



— longispinum, Sow. (fig. 67). 



Hoplites mammillaris, Schloth (fig. 69). 



Hoplites Deverianus, d'Orbig. (fig. ^9). 



— Rhotomagensis, Sow. 



— Mantelli, Sow. 



— Woolgari, Mant. 



