146 
globose, and others more compressed by age ; but they 
generally lose some of the ornaments from their last 
whorls, and in their infant state are also smooth, or free 
from tubercles, bearing some analogy to the higher 
orders of the animal creation, whose middle ages are 
generally the most beautiful. No species perhaps un- 
dergoes a greater change than the one before us, where- 
fore it is named mutabilis: 
AMMONITES subarmatus. 
TAB. CCCCVII. —Jig. 1. 
Spec. Char. Depressed, concave, ribed, in* 
ner whorls almost wholly exposed ; ribs 
curved, often united in pairs by smooth 
spines; aperture transversely oblong, 
arched. 
Syn. Ammonites subarmatus, Young a?id JBird, 
Geol. of Yorks* p. 250. t . 13,/. 3. 
Upon the last formed whorls of this shell, the spines dis- 
appear, and the ribs which in the former whorls are gene- 
rally split before they pass over the front, are not so 
often divided ; the spines continue nearly to the centre, 
they are hollow, and leave when the shell is removed, a 
blunt cast, but not a truncated tubercle as in the A. fibu- 
latus ; the whorls have convex sides and encrease rather 
rapidly ; they are contracted in some parts, in the same 
manner as the last. 
It is probable that there are several species allied to 
this, hut it will require numerous specimens of each to 
prove that they are not varieties : the A. perarmatusf of 
Young and Bird, is one thus doubtfully situated, but 
most probably it is a variety of the subarmatus. 
Found at Whitby. 
* It is hoped that the late Mr. Sowerby’s veracity and credit, need no 
defence against the attacks and false surmises of the arrogant, the Au- 
thors of the Geological Survey of the Yorkshire Coast, had not been 
further noticed, but that, when names are given to shells, their Publishers 
must be quoted, and where any merit exists, it should not be overlooked^ 
t We had not seen the Geol. of the Yorkshire coast, when A. perarma* 
tus, tab. 352 was published. 
I 
