78 
AMMONITES denarius. 
TAB. DXL .—fig. 1. 
Spec . Char. Discoid with a flat edge, a row of about 
10 tubercles on each side, and thirty curved 
radii abruptly terminating near the front ; 
whorls few, partly exposed ; aperture oblong. 
A rather compressed shell : the tubercles are conical, 
obtuse ; each of them is joined to two rays, and there is 
generally a third ray between each ; none of the rays ex- 
tend past the tubercles towards the centre ; they are all 
nearly equal, and a very little enlarged just before they 
terminate upon the front. 
Distinguished from A. lautus, tuberculatus, and seve- 
ral of the same division of the genus, by the blunt and 
low termination of the rays upon the front, and several 
minor characters. In the young state the aperture is 
longer than wide, and the tubercles only a little elevated. 
Found on Blachdown, by H. H. Goodhall, Esq., in 
whose cabinet the larger specimen is preserved. The 
shell is cast in silex. 
AMMONITES spinosus. 
TAB. DXL.— /g. 2. 
Spec. Char. Discoid, radiated ; whorls few, fur- 
nished, when young, with four rows of strong 
spines, which disappear by age ; radii nume- 
rous, forked, almost lost on the front ; inner 
whorls exposed ; aperture nearly round. 
There are about 20 spines in each row, each connected 
at its base with two or three rays ; they are gradually 
shorter after the shell has acquired an inch in diameter, 
and at length disappear : the radii are sharp but irregular. 
This is a remarkable instance of the change of orna- 
ment that Ammonites undergo as they increase in size, 
but still in unison with many others ; for it is very usual 
for Ammonites to become nearly plain when they have 
attained their full growth, and many are equally smooth 
in their youngest state. 
Casts in Pyrites are met with near Weymouth, and 
also in Clay at Braunston, as I learn from Miss Baker. 
