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bled closely Aucoini, but the abdomen becomes more prominent 

 and the contact furrow is deeper and broader in consequence of 

 this and the breadth of the venter. 



The siphuncle in the paranepionic substage issubventran, becom- 

 ing propioventran in the ananeanic as seen in section above in 

 Fig. 14, and extracentroventran in the septum seen below in Fig. 

 12. The position alters slightly in the succeeding stages. 



The living chamber is obviously over one-half of a volution in 

 length and is shown in an incomplete fragmentary condition in the 

 outline on the farther side of Fig. 12; the form in section of the 

 same specimen partly restored is given in Fig. 13, PI. iv. The 

 depth of the dorsal lobes in the sutures is shown upon the venter 

 of the exposed whorl in the upper part of the section which is still 

 covered by the dorsal layer and the remnants of the septa. 



Tarphyceras extensum. 



Loc, Port au Choix, Newfoundland. 



This fossil resembles Tarphyceras Seeleyi, but has a shorter living 

 chamber and the living chamber and part of septate whorl are free 

 in gerontic stage. The contact furrow increases in depth with the 

 ephebic stage and then decreases with the approach of the gerontic 

 stage. The ventro-dorsal diameter slightly decreases, as is shown 

 in Fig. 1, PL vi, in the paragerontic substage, when the whorl is 

 almost straightened out, and at the same time the impressed zone 

 is found to be wholly lost, as shown in the section, Fig. 2. 



In section 4 the inner whorl represents a section of the 

 ephebic stage and the outer whorl is the gerontic stage. The 

 uppermost, with siphuncle nearer the venter and reduced impressed 

 zone, is the anagerontic, and Fig. 2 is the paragerontic sub- 

 stage. The whorls are apparently smooth. The septa are not very 

 concave. The sutures have ventral saddles, dorsal lobes and slight 

 lateral lobes. In the anagerontic substage they are nearly straight 

 on the sides and decidedly inclined forwards. 



Tarphyceras Champlainense. 



Nautilus Champlainense, Whitfield, {Bull. Am. Mus., New 

 York, Vol. i, Figs. 1, 3, PL 31). 



Loc, Fort Cassin, Lake Champlain. 



PL iv, Figs. 4-1 1. 



The nepionic stage of this species, as in others of this group, has 



