THE NAUTILUS. Li 
A series of 76 multidentata from 13 localities and 45 lamellidens 
from 8 localities were measured. Where I had only a few from 
a given locality all were measured, but in the case of large series 
a few were picked out at random. These shells ran from 1.85 
to 3.28 mm. diameter in multidentata, 9 of them being 3.00 mm. 
diam. and over, and from 1.55 to 4.03 mm. diameter in lamelli- 
dens, 23 of them being 3.00 mm. and over. 
42 multidentata and 28 lamellidens, 2.50 mm. diameter and 
over, gave the following averages: 
V. multidentata av. diam. 2.79 mm., diam. umbilicus 0.51 mm. 
V. lamellidens av. diam. 3.39 mm., diam. umbilicus 0.39 mm. 
These averages show that the umbilicus is contained 5.5 times 
in the diameter of the shell in multidentata and 8.7 times in 
lamellidens. 
Another difference which is well shown in the figures is the 
angle made by the teeth and lamelle to lines drawn parallel to 
the lip and at right angles to it. 
The rows of teeth and the lamelle were counted in all of the 
121 shells measured and were found to vary from 1 to 4 in 
multidentata and from 0 to 3 in lamellidens. In both species 
there is a tendency to complete absorption in the fully adult 
shell and in my largest lamellidens, 4.03 mm. diam. from 
Thunderhead, Gt. Smoky Mts., I cannot distinguish a trace of 
the lamelle. <A Jlamellidens from Thunderhead has 4 lamelle, 
one of the apparently 3 being double. 
The largest multidentata have from 6 to 6.25 whorls while the 
largest lamellidens have 6.5 to 7. 
V. multidentata when adult has a well-defined callus connect- 
ing the end of the lip which is entirely absent in lamellidens. 
In both species the lip is slightly thickened when adult while 
in immature shells it is very thin and generally broken in cab- 
inet specimens which accounts for the apparent difference in 
the shape of the aperture of the shells figured, as it was very 
hard to trace. 
I believe that the figures and data given above prove that the 
two species are distinct and that the northern shells, though 
smaller, are the same as typical lamellidens from the southern. 
mountains. Compare Figs. 17 and 18, from the type locality, 
