﻿435 



lines of growth, which are more or less sporadic in shells of this 

 group. These primitive costae are probably due to the imperfect 

 resorption of the more or less expanded borders of the apertures 

 occurring in some shells but not in others during the progressive 

 stages of development but common in all shells in the gerontic 

 stage. 



The shell is very thick on the venter, somewhat thinner, but still 

 thick on the sides and dorsum. 



The type is Tarphyceras prematurum. 



The species of this genus are as follows : * 



Tarphyceras Aucoini, Hyatt, Newfoundland. 



prematurum , Hyatt, Newfoundland. 

 Famsworthi (sp. Billings, pars.), Phillipsburg.'j* 

 Champlainense, sp. Whitfield, Fort Cassin. 

 " Seeleyi, sp. Whitfield, Fort Cassin. 



" externum, Hyatt, Newfoundland. 



" MacDonaldi, n. s., near Lexington, Va. 



This last species has a form and suture like that of Champlain- 

 ense, but the siphuncle is nearer the venter and the young have 

 flatter and more divergent sides and broader abdomen in the neanic 

 stage. 



Tarphyceras Aucoini, n. s. 



Loc, Port au Port. 



PL iv, Figs. 17-22. 



The ananepionic substage seen in the somewhat rough casts is 

 given in Figs. 20-22, PI. iv, from the side and front. These figures 



* Nautilus caltiferous of Billings (Pal. Foss., i, p. 258) is probably a species of this genus 

 surviving in the later forms of the Quebec at Port au Choix. The small siphuncle and 

 its position appears to indicate this, but I have no specimens of this species and have 

 not seen any at Ottawa. 



-j-This species has two or more very distinct species. The one referred to above has an 

 elliptical or oval whorl in the ephebic stage, the dorsum a little broader than the venter. 

 There is a contact furrow in the neanic and ephebic stages. The sutures have ventral 

 saddles, with probably slight dorsal lobes in the zone of involution, and a free living 

 chamber over one-half of a volution in length. The siphuncle is subventran in the 

 ananeanic substage, becoming propioventran in the paraneanic and ventrocentren in 

 the metephebic substage. The diameter of the largest specimen, somewhat compressed . 

 was 140 mm. by 116 mm.; the estimated longest diameter of this through the tree living 

 chamber was about 160 mm. 



The type of Famsworthi is a very distinct species and belongs to another genus and \? 

 cited below under the heading of Aphetoceras. 



