THE NAUTILUS. 117 



A series of 76 multidentata from 13 localities and 45 lamelUdens 

 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 lamelUdens, 2.50 mm. diameter and 

 over, gave the following averages: 



V. multidentata &v. diam. 2.79mm., diam. umbilicus 0.51 mm. 



V. lamelUdens 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 

 lamelUdens. 



Another difference which is well shown in the figures is the 

 angle made by the teeth and lamella? to lines drawn parallel to 

 the lip and at right angles to it. 



The rows of teeth and the lamella? were counted in all of the 

 121 shells measured and were found to vary from 1 to 4 in 

 multidentata and from to 3 in lamelUdens. In both species 

 there is a tendency to complete absorption in the fully adult 

 shell and in my largest lamelUdens, 4.03 mm. diam. from 

 Thunderhead, Gt. Smoky Mts., I cannot distinguish a trace of 

 the lamella?. A lamelUdens from Thunderhead has 4 lamella?,, 

 one of the apparently 3 being double. 



The largest multidentata have from 6 to 6.25 whorls while the 

 largest lamelUdens 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 lamelUdens. 

 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 lamelUdens from the southern 

 mountains. Compare Figs. 17 and 18, from the type locality ,, 



