THIRD, OR VERMICERAN BRANCH. 155 
The young whorls for a very limited stage are smooth, then the rounded 
abdomen and immature pile of Caloceras appear. The keel is introduced after 
this stage, and we have for a stage of greater or less duration, according to the 
species, a resemblance to somé varieties of Caloceras laqueum. 
The adults are characterized by quadragonal forms and flattened, keeled, and 
channelled abdomens. The pile are straight, with distinct genicule bending 
forwards. In one variety of Verm. Conybeari the genicule are tuberculated, in 
other examples they are smooth. 
The sutures have arietian proportions in the adults, though they retain the 
immature proportions of the young until a late period of growth, and often even 
in the adult stage. The abdominal lobe is longer than the superior laterals, and 
the superior lateral saddles shallower than the inferior laterals; the auxiliary 
saddles and lobes may occasionally have a backward trend in the young, but this 
is not found in adults. 
The old stage retains the keel, and has smooth, somewhat flattened and con- 
vergent sides. This is very distinct from the similar stages of Caloceras, in which 
the keel is lost and the whorl becomes rounded. The extreme form assumed in 
old age, when contrasted with the adult whorl, can be best described as trigonal. 
It is, however, still similar to the senile stages of Caloceras before the keel is lost, 
and the sides are more gibbous than in the trigonal senile whorls of the more 
highly developed species of Coroniceras. The sutures degenerate, the abdominal 
lobe becomes shorter. Our observations on the geratologous period in this 
genus were not so satisfactory as in some others, senile specimens being of rarer 
occurrence. Quenstedt, in his “ Amm. Schwab. Jura,” Plate VIL, figures under 
the names of brevdorsalis and brevidorsalis macer several fragments of large shells, 
which are probably examples of senile metamorphoses belonging to this genus, 
but we are not able to designate the probable species. Although the last whorls 
are represented as perfectly smooth in these figures and the sides convergent, 
and the abdomen considerably narrowed, the keel and channels are still persistent. 
The whorl in the oldest specimen had become so excessively altered by senile 
degradation that it was smooth and helmet-shaped, as in Psiloceras, and the 
channels obsolescent, though a low broad keel still remained. 
There is also in the British Museum a fossil, 1010 mm. in diameter, labelled, 
“Zone of A. planorbis and Pent. tuberculatus, Newbold Quarries, Rugby, Warwick- 
shire.” This has the outer whorls compressed and smooth, as in Psi. planorbe, but 
with a keel and obsolescent channels preserved on part of the last volution. We 
identified this as an aged specimen of Verm. Conybeari, but eminent paleontologists 
in England have expressed their opinion that it might be a specimen of planorbe. 
We are much indebted to Mr. Henry Woodward, of the British Museum, for a 
large drawing of this fossil, but unfortunately this is not sufficient to settle the 
questions involved. We have had no opportunity for re-examination, and should 
have considered our former opinion as probably erroneous but for other evidence. 
According to Wright, Pentacrinus tuberculatus is not found below the Angulatus 
bed in England. We have also seen in the rock at Lyme Regis sections of old 
whorls of Conybeari closely resembling this, and also a still more advanced stage, 
