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ceras (PL vi, Fig. 5) with the figure of the young of Pycnoceras 

 apertum (PL v, Fig. 18). The nepionic stage has rounded dorsum 

 and more rounded venter than appears in the Fig. 19, PL vi, be- 

 cause of the presence of a thick band of shell on the venter, con- 

 sisting of its own shell which is not present on the sides and also 

 of the corresponding part of the shell of the dorsum of the next 

 older whorl that has been broken away. A slight contact furrow 

 is present at the beginning of the ananeanic substage when the whorls 

 come in contact at the point indicated in Fig. 18 by the end of the 

 outline of the restored apex. This zone is further shown by the 

 band of shell left on the venter from the dorsum of the next older 

 whorl, which was the neanic volution. Upon this, also, there are 

 remnants of the septa of this stage, showing that this zone was 

 immediately accompanied by the advent of dorsal lobes in the 

 sutures. These replaced the dorsal saddles of the nepionic stage. 



In the ephebic stage the siphuncle assumed a propioextraventran 

 position and retained this until the gerontic stage. 



The form of the whorl remains quite similar, the ventro-dorsal 

 diameters being longer than the transverse, but the venter becomes 

 broader in proportion than the dorsum in neanic and ephebic 

 stages. 



In the gerontic stage the living chamber and part of the septate 

 last whorl alone are free in some species, in others the age at which 

 the whorl becomes free varies greatly. 



The type of the genus is the young specimen, Fig. 18, which 

 shows that the young are distinct from those of Tarphyceras, being 

 much less closely coiled and having distinct form of whorl and 

 large umbilical perforation. 



There are several undescribed species of this genus in the fauna 

 of Newfoundland. 



Pycnoceras apertum, n. s. PL v, Figs. 18-20. 



Loc, Port au Port, Newfoundland. 



This single specimen was found in the dolomitic limestone or 

 calciferous in company with the closer coiled young of Tarphyceras. 



The nepionic stage is prolonged and has the oval form of whorl 

 and sutures of the adults of the cyrtoceran genus, Melon oceras, and 

 of the nepionic and neanic stages of the gyroceran form, Apheto- 

 ceras, its nearest affine, which occurs, however, later in the fauna 

 of the Quebec group. 



