533 
lines of growth and the dorsal sutures are not correctly given. The 
dorsal lobes exactly coincide with the impressed zone in Fig. 6 of 
his plate. This figure shows the last part of the paranepionic volu- 
tion in section below and the ananeanic with the impressed zone 
above this. The smoothness of the impressed zone in Hall’s Fig. 6 
of this species shows that the longitudinal ridges were obliterated 
as they are in other forms by the pressure of the growing whorl, 
and that this zone is probably due to contact and did not occur on 
the free side of the volution in the umbilical perforation. I use 
the general term ‘‘impressed zone,’’ because, although my notes 
and Hall’s observations and the figures all seem to warrant the 
statement that this zone in this species is a contact furrow, I have 
not been able to revise and confirm these observations. 
NEPHRITICERAS BUCINUM. 
NAUTILUS BUCINUS, Hall (Pa/. WV. V., v, Pt. ii, Pl. Ix). 
The paranepionic volution is shown in Hall’s Fig. 1, Pl. lx, with 
a convex dorsum, and in Pl. cvii, Figs. 2 and 3, it is again shown 
with the siphuncle dorsad of the centre and the outline distinctly 
subtrigonal. ‘These figures indicate great variability in the time 
at-which the impressed zone appears, since the section in Pl. cvii is 
very much larger than that of about the same age of Fig. 2, Pl. Ix. 
One is disposed to think that these are perhaps different species. 
Fig. 2 of Pl. lx gives in front view a section of the paranepionic 
volution with a distinct but narrow impressed zone marked on the 
dorsum, ‘This whorl has a nephritic outline and is very different 
from the subtrigonal outline of a whorl with convex dorsum referred 
to above, which belongs to an obviously later stage of growth in a 
larger species. 
Having examined these specimens in Prof. Hall’s collection some 
years since, I find in my notes the statement that ‘‘ no depression 
(meaning the dorsal furrow) occurs in the centre of any of these 
shells until the whorls touch, which they do at a late stage of 
growth.’’ The form changes from a depressed oval in the metane- 
pionic to nephritic more rapidly than in Wephriticeras subliratum 
and the transverse diameters increase faster. The longitudinal 
ridges are smaller and less prominent than in Wephriticcras liratum. 
The sutures in the young have ventral and dorsal saddles and 
only in later stages these are replaced on the dorsum and venter by 
