214 
constantly increasing ribs, with a number of tubercles, which 
adorn the sides and border. The siphonal area presents many 
differences; sometimes the median line is channelled, with rows 
of tubercles on the border, so that the ribs are interrupted 
= ~= 
GINS 
Fia. 75.—Acantho. laticlavium, Sharpe. Fie. 76.—Acantho. Brottianum, d'Orb 
from crossing; in other species the channel is wanting, and the 
ribs pass across. Sometimes the tubercles arrange themselves 
in a series of rows, or pass along the median line and form a 
kind of knotted keel. The suture line presents considerable 
variety in these highly ornamental shells. The siphonal and 
principal lateral lobes are about the same size, sometimes the 
former is much larger than the latter; and the second lateral is 
much smaller than the first, both terminate in single fronds, 
and there are several auxiliaries. 
All the species are Cretaceous. 
Acanthoceras Brottianum, d’Orb. Acanthoceras Mantelli, Sow. 
" Deverianum, d’Orb. u Rhotomagense, Brong. 
mammillare, Schl. " Sussexiense, Sharp. 
Martinii, d’Orb. " Woolgarei, Want. 
All these species have been separated from Hoplites, and 
some of them have appeared under that generic name in the 
earlier part of this Monograph. They are, however, now placed 
as indicated by the author in his latest work on this subject. 
Genus Sroticzxata, Newm.—Has been erected to receive a 
small group of remarkable Ammonites figured and described 
by Dr. Ferp. Sroriczxa in his great work on the Ammonitide 
from the chalk rocks of Southern India, some of which were 
