1911.] 



NATURAL SCIENCES OF PHILADELPHIA. 



153 



in any way. The only semi-fossil shell among the Benmore woods 

 specimens has the highest spire of any measured, it gives 25 x 4(H mm. 



The shells in this colony are smaller than those in the Kendal Road 

 colony, and they are higher in the spire proportionately, or the index 

 is slightly higher. There are none of the dimensions of the largest 

 from Kendal Road colony, but one approaches it (22x44^ mm., as 

 against 21 x 46 mm. from Kendal Road) and this has an index of 

 .495, the only one with an index under .50. 



Fig. 12 shows the distribution of size in this colony, the dimensions 

 of the 42 specimens measured being given to the nearest whole milli- 

 meter. The frequency curve for widths shows that the majority 

 range from 37 mm. to 40 mm., with a slight drop in the curve at 39 mm. 

 The curve of heights shows a strong maximum at 22 mm. 

 Pleuredonte acuta goniasmos A. D. B. Plate XI, figs. 8, 9. 



At Cedar Hill wood colony. 



Shell generally rather elevated, consisting of 5 to 5A whorls, in some 

 cases slightly excavated above the periphery on the last whorl, espe- 

 cially in the higher forms otherwise convex at this point; with an 

 index varying from .472 to .656, but in 69 per cent, of the specimens 



■10 



.».--•-- 



Fig. 13.— Cedar Hill. 



it runs between .50 and .60 and is distributed as follows: under .50 

 in 4 specimens, .50-55 in 13, .55-. 60 in 16 and above .60 in 7 specimens. 

 Three of these 7 specimens are very large semi-fossil shells, measuring 

 40 to 4H mm. in diameter, the other 4 are small, very high shells of 

 the fresh, living series, and range in size from 21 x 32 mm. to 225 x 36 

 mm. In the diagram of the measurements of this colony (fig. 13) 



