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Plate VI. 



Figs. 1-4. Tarphyceras externum, Quebec Group; Loc, Port au Choix, New- 

 foundland. Reduced one-third. Fig. 1, lateral view, showing position of siph uncle, 

 septa in section and free volution. Fig. 2, section of living chamber at the ter- 

 mination restored by observation of the more perfect parts of the same volution. 

 Dorsum appeared to have no impressed zone in this obviously the gerontic stage. 

 Fig. 4, section of two ephebic whorls in part restored, showing impressed 

 zone and general form. Fig. 3, section of younger whorl, restoration in part. 

 Dimensions are incorrect in these sections, but the form is correct. 



Figs. 5-8. Aphetoceras Americanum, Quebec Group; Loc, Port au Choix, 

 Newfoundland. Reduced one-third. Fig. 5, side view showing gyroceran mode 

 of growth, suture with ventral lobe and younger sutures with ventral and dorsal 

 saddles. Fig. 7, section of the outer whoil. Figs. 7, 8, sections taken at the 

 two contiguous breaks in the outer and next inner whorls. Dimensions of these 

 sections are not correct, but form is properly represented. 



Figs. 9-1 1. Litoceras insolens (?) (sp. Bill.), Hyatt, Quebec Group; Loc, 

 Gargamelle Cove, Newfoundland. Fig. 9, side view of young specimens, very 

 nearly natural size. Fig. 10, interior whorls enlarged to show large umbilical 

 perforation, costations of metanepionic, paranepionic and ananeanic substages, 

 and the loose coiling of the ananeanic substage. Fig. 11, section of nepionic, 

 ananeanic and anephebic volutions showing the absence of impressed zones in 

 the nepionic and changes of form in older whorls. Compare this with the young 

 of Trocholiioceras Walcotti. 



Figs. 12-20. Trochohtoceras Walcotti, Quebec Group; Fort Cassin; U. S. 

 Nat. Museum, Walcott Coll. Fig. 12, side view of type specimen natural 

 size. Fig. 13, section of same. Fig. 14, section of centre of same enlarged to 

 show the largest diameter of the umbilical perforation and the ananepionic sub- 

 stage and paranepionic with impressed zone. Fig. 20 gives location of this section 

 and all the rest are taken between the two bisecting lines of this figure. Figs. 15- 

 19, successive sections gradually passing out of the umbilical perforation and 

 showing the position of the siphuncle and increasing depth of the impressed zone 

 after contact These sections also show that the impressed zone occurs after the 

 gyroceran bend in the beginning of the paranepionic substage, and is apparently 

 a result of the great increase in transverse diameters, nephritic form of whorl 

 and abrupt bending. Fig. 20, location of sections, ideal. The shape of the ana- 

 nepionic volution in Fig. 13 is more accurate than in Fig. 14 or 15. 



Figs. 21-27. Schroederoceras teres (sp. Eichw.), after Holm, Pal. Abh. Dames 

 et Kayser,\\\,Y\. v. Figs. 21 and 22 show the subventral caecum in apical 

 chamber and shifting of position to dorsad of centre in the ananeanic substage. 

 Compare with Schroederoceras Eatoni, Fig. 35. Figs. 23-27, ananepionic, 

 metanepionic substages, the septa belong wholly to the metanepionic. There is 

 no dorsal furrow in this shell until the third septum is reached and by comparing 

 this with sections, Figs. 21 and 22, it is seen that this indicates either the begin- 

 ning, Fig. 21, or the completion of the gyroceran bend, Fig. 22, although Holm's 

 Fig. 25 would lead to the supposition that the bending had not yet begun. 



Figs. 28-35. Schroederoceras Eatoni, sp. Whitf., Hyatt, Quebec Group; Loc, 



