436 
show the apex to be blunt and rounded, but this rotundity may be 
exaggerated in this part which had to be in part restored. 
The umbilical perforation is present, but it is very small. The 
whorl grows very rapidly in all of its diameters and the bending of 
the shell in the paranepionic substage is very abrupt, bringing the 
continuation of this substage, the dorsum, in contact with the dor- 
sum of the metanepionic and ananepionic parts of the first volu- 
tion. 
In correlation with this, as in Trocholites, a distinct dorsal fur- 
row appears as the shell bends in the first part of the paranepionic 
substage. The coiling is so close that the slightest variation in the 
same direction would obliterate the umbilica) perforation. The 
growing mantle while building the shell might have been influ- 
enced by the proximity of the metanepionic dorsum and the small 
diameter of the curve. ‘The dorsal furrow here, as in Trocho- 
lites, although occurring in the paranepionic substage before the 
whorls touch, is perhaps due to the close contiguity of the whorls 
and the rapid ingrowth of the primitive umbilical zones. This 
process is still apparent in the first part of the second whorl, a sec- 
tion of which is given immediately above the apex in Fig. 20. 
This is the first of the ananeanic substage, and the siphuncle shifts 
from its previously subventran position to propioventran. In the 
metaneanic substage, in the latter half of the second volution, the 
elongation of the ventro-dorsal diameters is faster, and the ten- 
dency to develop lateral zones by the flattening of the sides becomes 
marked. ‘The sections of the whorls in the upper half of Fig. 20 
are slightly distorted by compression, the lower half is in proper pro- 
portion. The aspect of the section is better given in the more 
enlarged Fig. 21, and the decrease in lateral diameters in proportion 
to the ventro-dorsal is a marked characteristic and continues in the 
ephebic stage. 
In some specimens this change is not so marked and the flatten- 
ing of the sides develops later. 
In the later stages the siphuncle is slightly nearer the center as in 
Fig. 19. 
Fig. 17 gives the full-grown ephebic stage, and is very close to 
the original. The section Fig. 19 shows bow closely this species 
resembles Zarphyceras Champlainense, differing only in the greater 
rotundity of the venter and in the position of the siphuncle and in 
