23 
AMMONITES Sowerbii. 
TAB. CCXIII. 
Syn. A. Sowerbii. Miller MSS. Catalogues. 
Spec. Cuar. Discoid, carinated, with about eight 
spiniform tubercles upon each whorl ; keel de- 
fined, entire ; aperture elliptical. 
Var. 6 aperture circular, keel sometimes impressed. 
ee 
Voxurions about four, the inner ones concealed to the 
bases of the tubercles; the outer part of the volutions 
has many gentle undulations ; the inner part is even, 
except that the base of each tubercle is extended towards 
the centre in an obtuse ridge. The keel nearly sepa- 
rated from the body of the shell ; it is round and entire. 
In var. 6 the ridges from the bases of the tubercles are 
more prominent, and the keel sometimes so far sunk as 
to have a furrow on each side of it. The inner whorls of 
var. a appear to be more gibbose than the outer ones. 
Mr. Miller considers the shell figured as one of his 
rarest specimens : his collection has also to boast of seve- 
ral smaller specimens, belonging to var. 8, which vary 
in the gibbosity of the whorls; they were all found at 
Dundry, in the Inferior Oolite. 
