THIED, OE VEEMICEEAN BEANCH. 155 



The young whorls for a very limited stage are smooth, then the rounded 

 abdomen and immature pilae 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 some varieties of Caloceras laqueum. 



The adults are characterized by quadragonal forms and flattened, keeled, and 

 channelled abdomens. The pilae are straight, with distinct genicular bending 

 forwards. In one variety of Verm. Gonybeari the geniculse 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 VII., figures under 

 the names of brevidorsalis 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 Psil. planorbe,but 

 with a keel and obsolescent channels preserved on part of the last volution. We 

 identified this as an aged specimen of Verm. Gonybeari, 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 Gonybeari closely resembling this, and also a still more advanced sta^e, 



