﻿477 



The types were not to be found in the museum at Ottawa during 

 my visit to that museum several years ago. 



The young of this species increases in the transverse diameters with 

 great rapidity. The ananepionic stage, Figs, 9, 10, PI. vi, has the 

 usual straight, fine strise and the metanepionic and succeeding sub- 

 stages throughout the first, and a part of the second whorls have 

 the costations which are common at the same age in other shells of 

 this family. The umbilical perforation is of considerable size ; the 

 whorls change from the rounded, cyrtoceran form of the anane- 

 pionic substage, which apparently has the ventrodorsal longer 

 than the transverse diameters, very rapidly as the gyroceran stage 

 approaches on the latter part of the first half of the first whorl or 

 the metanepionic substage. In the paranepionic on the last half 

 of the first whorl and before the whorls touch, the whorl is like the 

 metanepionic volution as shown in section in Fig. n, PI. vi, trigo- 

 nal, the venter broader than the dorsum, and the angles are rounded. 

 In the ananeanic substage, after the completion of the first whorl, 

 the whorl becomes digonal, with a contact furrow. Near the end 

 of the first whorl, in the paranepionic substage, the ventro-dorsal 

 diameter was 3 mm., roughly measured; the transverse through the 

 abdominal angles were approximately 6 mm. ; half of a volution 

 beyond this, in the ananeanic substage, the transverse had become 

 10 or 11 mm., and the ventro-dorsal about 6 mm. ; less than one-half 

 volution later in the paraneanic the transverse had become 16 mm. 

 and the ventro-dorsal about 7 mm. ; somewhat more than one-half 

 volution later, in the anephebic substage, the whorl had become 

 changed to kidney shaped in section, and the septum at the base of 

 the living chamber was exposed. The transverse diameter was 

 29 mm., the ventro-dorsal 12 mm., both taken without the shell. 



Fig. 11, PI. vi, shows a sectional view of the metanepionic, 

 neanic and ephebic volutions. The diameters through the umbili- 

 cal zone, parallel with the mesal plane, were equal or about the 

 same, roughly measured, as the ventro-dorsal diameters. 



The anaphebic sutures of the septum at the base of the living- 

 chamber in the specimen figured has a well-marked median saddle, 

 narrower than in a full-grown shell, and on either side of this were 

 faintly marked ventral lobes. These last were continued on the 

 sides, rising steeply to the umbilical zones, where they culminated 

 in broad saddles. These descended abruptly in the contact fur- 

 row, forming a broad, deep, dorsal lobe. These sutures are quite 



