1911.] NATURAL SCIENCES OF PHILADELPHIA. 137 



The periphery on the last whorl is not angled nor keeled, but is evenly 

 rounded. The range of size in the 18 specimens examined varies but 

 slightly, and the form is nearly the same in all (it is a rather homoge- 

 neous colony) and the average dimensions are: height 30 mm., width 

 54 mm., index .555. Mean divergence about 120°. While the young 

 shell is strongly keeled, this sharp angle of the periphery of the shell 

 is completely lost at 4^ whorls, so that no angle appears along the 

 periphery on the last whorl. The umbilicus is normally closed by an 

 expansion of the lip, but in two shells (one of which is damaged) the 

 expansion does not entirely cover the umbilicus. 

 Pleurodonte bainbridgei Pfr. Plate VIII, figs. 5, 6. 



At the Garrett's woods colony. 



Shell with a moderately depressed spire, the outline of which is 

 somewhat concave to linear, with 5j whorls, of which the last is only 

 slightly depressed along the suture in the last ^, or in some cases not 

 at all depressed; the periphery is slightly angled on the last whorl 

 up to within \ whorl of the end or in one or two cases up to the end, 

 otherwise rounded in the last \ whorl, and resembling the more de- 

 pressed specimens from the Ridge near Lincoln. Umbilicus completely 

 closed by the expansion of the lip in all of the specimens. The average 

 dimensions are: width 53.3 mm., height 29.6 mm., index .555, mean 

 divergence 125°-135°. Number of specimens, 10. 



Pleurodonte bainbridgei Pfr. Plate VIII, figs. 7, 8. 



At the Benmore colony. 



Shell with depressed spire, consisting of 5 whorls or less, with a 

 suture that is not at all impressed or only impressed on the last j 

 whorl; the periphery of the shell is slightly angled to the end of the 

 last whorl, this being caused by the last whorl's being somewhat flat- 

 tened on that part just above the periphery and sloping away rather 

 sharply below. The umbilicus is closed by an expansion of the lip. 

 The dimensions are: width 50f mm., height 27^ mm., mean divergence 

 about 125°, index 54. 



Pleurodonte bainbridgei Pfr. Plate VIII, figs. 9, 10, 



At the Cedar Hill colony. 



Shell with rather depressed spire, consisting of 4| to 5 whorls; 

 the suture on the last | of the last whorl scarcely at all depressed, 

 and this part of the whorl rounded at the periphery and scarcely 

 angled beyond 4^- whorls. The umbilicus is generally completely 

 closed, but in two specimens it is only about § closed by the expansion 

 of the lip. Average dimensions are: width 52 mm., height 26.7 mm., 

 mean divergence 140°, index .515. 



