230 PROCEEDINGS OF THE ACADEMY OF [Mch., 
sculpture is less strong except just behind the lip, where the wrinkles 
generally are emphatic. 
The lot of smaller specimens (PI. XII, figs. 9-13) consisted of about 
300 shells. 200 fully adult specimens were measured. The diameter 
varies between 13 and 17 mm., and gives the curve plotted on p. 229. 
The major mode is at 15 mm., 43 per cent. of the lot being within .2 
mm. of that dimension. There is a minor mode at 14 mm.; but the 
lot is remarkably homogeneous, since over 80 per cent. are between 
13.8 and 15.2 mm. diameter. 
The altitude bears no constant ratio to the diameter. It is individu- 
ally variable within wide limits. In the first 50 individuals of 18 mm. 
diameter (from my schedule of measurements of 200 specimens of all 
sizes) the following dimensions were found: 
Alt. in mm., 8 fae 80° | 8.7 8.8 se Dae 9.2 
No. of variates, 3 2 3 3 5 3 15 2 
Alt.inmm., Pees). 9:5 9.6 98:7) O8aae 10.2 
No. of variates, 1 2 1 2 2 1 1 
3 
Alt. in mm., 10.6 
No. of variates, 1 
It will be noticed that the mode is at 9 mm., 30% of the whole num- 
ber having that altitude, while the number of more depressed individ- 
uals is as nearly as possible equal to the number more elevated. Speci- 
mens of the same lot, of other diameters, give altitude curves of the 
same symmetrical form, and need not here be detailed. 
There are 5 albinos in the 200 shells measured, though an uninter- 
tupted series from albinos to the darkest brown specimens makes a 
selection difficult. 
Nine shells in 200 show a very small parietal tooth, one being shown 
in fig. 12. 
The other lot, of larger shells (Pl. 12, figs. 7, 8), contains 2 albinos 
out of 14 shells. None has a parietal tooth. The measurements 
follow: 
Alt., 12 dt 10 10.3. TOS ao 10 10 10 
Diam., 19.3 19 19 18.5. 183 183 182° is 17.5 
Alt., 10 10 92 9.2 mm. 
Diamine ae 16.8...“ 
A small series from Clouderoft, 8,750 feet, collected by E. O. Wooton, 
received from Prof. Cockerell, contains also large and small examples, 
