1911.] 



NATURAL SCIENCES OF PHILADELPHIA. 



147 



Road colony. The measurements of the specimens from this colony- 

 are given in fig. 8. 



Fig. 8. — Ridge near Lincoln. 

 Pleurodonte acuta goniasmos A. D. B. Plate X, figs. 5-7. 



At Garrett's woods colony. 



Shell varying much in size and relative dimensions of height and 

 width, but in general resembling the form of the higher shells from 

 the Ridge near Lincoln colony; consisting of about 5 whorls, convex 

 above and below the periphery on the last whorl; with a distinct 

 angle along the periphery and, in some cases in the larger shells, with 

 a slight concavity above the periphery in the last whorl. The index 

 varies, the lowest being .48 and the highest .655, but a very large 

 proportion of the specimens have an index of .55-. 58 and the average 

 for the typical specimens selected was .565. The plotting of the 

 heights shows 22 specimens with a height of 19.5 mm., 20 with a 

 height of 20 mm., 14 with a height of 20.5 mm., and 9 with a height 

 of 21 mm.; the extremes of height range from 17 mm. to 27 mm. in 

 the 83 examples measured, but these include 4 specimens which are 

 semi- fossil, the largest of the series. The fresh shells run from 17 mm. 

 to 23 mm. in height, these four semi-fossil ones from 24.5 mm. to 

 27 mm. The widths vary from 31.5 mm. to 40 mm. for the fresh 

 shells and the four semi-fossil shells range from 40 mm. to 44 mm. 

 The living forms show a sharp maximum in width at 36 mm., with 

 24 specimens (including those which measure 36.5); altogether 42 

 specimens range between 35 mm. and 37 mm. inclusive. The labrum 



