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 perpendicidar surface. 
Fig. 64. — Slepkanoceras coronatum, Brug. Fig. 65. — Steph. coronatum, Brug. Fig. 66. — Stephanoceras 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 arras, 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). 
— modiolare, Lhwyd. 
Stephanoceras macrocephalum, ScMoth. 
— 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 tlie 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 Aeg. Keiileyi occur in the Middle Lias, and Aspidoceras longispimm (fig. 67) in 
the Oxford clay. HopUtes mammillaris (fig. 69, 70), 11. Bhotomagensis, H. Mantelli, and 
Fig. 67. — Aapiduceras longi- 
spinum, Sow. 
H. Woolgari represent Cretaceous forms. 
Aegoceras Birchii, Sow. 
Aspidoceras perarmatum, Sow. 
— longispinum. Sow. (fig. 67). 
Hoplites mammillaris, Schloth (fig. 69). 
The following are typical species : 
Hoplites Deverianus, ffOrhlg. (fig. 79), 
— Rhotomagensis, Soio. 
— Mantelli, Sow. 
— Woolgari, Mant, 
