﻿571 



before the retroversal gerontic stage begins. The apex does not 

 exhibit any indications that the species had an excentric young 

 stage even at the'small diameter of 5 mm. in one specimen. There 

 appear to be no tubercles on the earliest whorls examined, probably 

 the neanic stage.' Two irregular rows of tubercles are introduced in 

 the ephebic stage with alternating untuberculated costae. The 

 tuberculated costae are sometimes bifurcated, and sometimes single. 

 The costae are closely set, subacute ridges, with concave flutes 

 between them both, arching apically, the flutings broader than the 

 costal ridges, but the surface is otherwise smooth. 



The height of the coil is over 40 mm. in the largest specimen, 

 through the ephebic whorls, although the apex is imperfect. In two 

 other specimens this length is much less, although the number of 

 the whorls is about the same. The diameter of this specimen 

 through the parephebic whorl is 34 mm. The height (transverse 

 diameter) of the parephebic substage is 19 mm., the ventro-dorsal 

 diameter about 13 mm. The diameter of the umbilical opening 

 must have been less than 12 mm. 



The costae are wider apart in the last of the ephebic stage, or par- 

 ephebic substage, and I expected to find that they died out altogether 

 for a certain space, but there was no evidence of this. They, how- 

 ever, appear to be slightly more prominent on the gerontic volution 

 than on the parephebic substage. 



The contact furrow begins early, being present on the smallest 

 whorl examined. There is therefore no positive indications that 

 this species had uncoiled or excentric young as in Emperoceras. 



In the anagerontic substage the whorl bends downwards or orally 

 in two dextral specimens, and in the metagerontic acquires larger 

 tubercles and coarser costae, sometimes bifurcated, and bends 

 upwards towards the base of the ephebic volution, forming the 

 retroversal living chamber. The last part of this, or the parage- 

 rontic substage, is nearly or quite straight, the bifurcations disappear, 

 leaving the costae straight, and the tubercles also gradually disap- 

 pear. The latest senile substage is also nearly if not quite bilaterally 

 symmetrical and strongly contrasts in this respect with all the stages 

 preceding the metagerontic substage. The return to the symmet- 

 rical form of whorl really begins in the metagerontic substage. The 

 living chamber has an aperture in one specimen. This is straight 

 across the venter, has slight crests on the sides, and is straight or 

 with very slight crest on the dorsum. 



