154 PROCEEDINGS OF THE ACADEMY OF [Feb., 



the six semi-fossil shells are readily picked out, as they are seen to be 

 the largest in the series. There are all gradations between the very 

 high spired type and those which are moderately elevated only, but, 

 as will be seen from the indices given above, only a very small number, 

 less than 10 per cent., have an index near that of the Somerset normal 

 forms or the flatter ones from Kendal Road colony. 



Average dimensions are height 21 mm., width 37 mm., index .568; 

 mean divergence varying from 90°-95° up to 105°-110°. The widths 

 vary from 32 mm. to 43^ mm., but 29 of the shells (69 per cent.) have 

 widths varying from 35 mm. to 39 mm. The heights also fluctuate 

 widely, depending upon whether the shell has the more depressed or 

 more elevated form. 



The shells of this colony are both one-toothed and two-toothed forms, 

 but the one-toothed form predominates and where two teeth are 

 present they are of very unequal size, the outer one being well-developed 

 and the inner one very rudimentary. More than 67 per cent, of the 

 specimens have only the outer tooth developed, the rest have the 

 outer quite large, but the inner one small. The number of examples 

 studied was 42, and their dimensions are given, with their frequency 

 curves, in fig. 13. 



Pleurodonte acuta goniasmos A. D. B. Plate XI, figs. 10, 11. 



At King Edward Hotel wood colony. 



Shell more uniformly elevated than in any other colony, consisting 

 of 5 to 5 j whorls; the last whorl convex above and below, next to 

 the periphery ; very rarely is there a trace of excavation at this point. 

 The whorls are somewhat convex above in those inside of the fifth 

 whorl in some cases, in others the spire is more straight on the slope. 

 The index runs uniformly higher than in the shells from the other 

 colonies examined ; in only one case out of 63 specimens does the index 

 fall below .50 (to .487) and only 12 are below .55; that is, only 19 per 

 cent, of the specimens examined. Of the rest, 31 specimens, or 49 

 per cent., are between .55 and .60; 19 specimens, or 30 per cent., have 

 an index between .60 and .65, and one exceeds .65, being .658. In all, 

 81 per cent, show an index of .55 or above, and the average index for 

 the colony is .585, much higher than any other examined. The shells 

 of this colony do not vary in size quite so much as in some others; 

 the extreme range of size is between 20 x 32 mm. and 23 x 42 mm.; 

 most of them run between 21x35 mm. and 23x40 mm. The 

 shells are prevailingly two-toothed, of the entire number .examined 

 in regard to this character, 68 in all, those with two teeth number 

 55 or 81 per cent, and the two teeth are both well-developed, although 



