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taken, is given in Fig. 31, PL vi. The core of the umbilical per- 

 foration was exposed, the metanepionic volution is smaller and 

 younger, the paranepionic section is older and is shown to be con- 

 vex on the gyroceran turn or curve around the core. The state of 

 the section left this observation open to some doubt owing to the 

 fact that it was slightly clipped on one side, exposing an older part 

 of the same whorl. On wearing this same section down a shade 

 farther the beginning of a dorsal furrow became apparent, and 

 is given in Figs. 32, ^s- 



It is, however, obvious that the dorsal furrow is very slight and it 

 occurs in the usual place on the paranepionic dorsum; the rotundity 

 and form of the metanepionic whorl was perfectly well defined. The 

 umbilical perforation in this fossil was very small, and the occurence 

 of a dorsal furrow at the place designated in the drawing could be 

 accounted for as due to the contiguity of the dorsum of the grow- 

 ing whorl of the paranepionic to that of the stiff wall of the 

 metanepionic substage. 



The position of the siphuncle in the apex could not be deter- 

 mined, but its place in the other whorls was plainly seen and 

 agrees closely enough with the positions determined by Whitfield 

 in the young of Eatoni, with which also the characters of the 

 sutures of the older whorls agreed in this specimen. 



The contact furrow is deeper relatively in the neanic stage 

 than it is subsequently, when one takes into account the form of 

 the whorl and the relative extent of the sides covered by involu- 

 tion. It is, however, very well marked in all stages, and its disap- 

 pearance upon the latter part of the last whorl, as has been shown 

 in Whitfield's figures and those given in this paper, is a significant 

 and instructive fact that has been discussed in other parts of this 

 essay. The aperture of Fig. 7, PL vii, was removable, and this 

 being taken off the last vestige of the impressed zone is seen on 

 the dorsal side of the free whorl in the front view of the same 

 specimen, Fig. 8. The portion removed is so short that it is pos- 

 sible it may represent the rim of the aperture itself. 



The sutures of the anephebic stages differ considerably from 

 those of the adult, being straighter and more like those of Trocho- 

 lites, and it may be questioned whether this should not be called 

 the paraneanic substage on account of its close resemblances to 

 Trocholites. 



In the full-grown shell of the parephebic and gerontic age, as 



