1911.] NATURAL SCIENCES OF PHILADELPHIA. 135 



hi fig. 3 a similar comparison of the Garrett's woods forms with 

 those from the Ridge near Lincoln is given. Here again there is no 

 mingling of the two groups and the frequency curves for width do not 

 overlap, but those for height do so slightly. In plotting all the fre- 

 quency curves the half-millimeter measurements were distributed to 

 the nearest whole millimeter. 



The variation here shown indicates that the Ridge near Lincoln 

 and Somerset colonies are much alike, and indeed these two localities 

 are connected by nearly continuous woods, but the smaller forms 

 from Garrett's woods have been living here for years since their isola- 

 tion by the clearing of the woods and have become a smaller race in 

 this time. The forms from nearer Mandeville were larger than those 

 from the isolated Garrett's woods colony. 



Pleurodonte bainbridgei Pfr. Plate VIII. 



Of the large series of this species in the collection of the Academy 

 of Natural Sciences there are two specimens from Mt. Diabolo, St. Ann 

 Parish, which are stated by Jarvis to be typical of the species. They 

 are evidently the extremes of the series found at this locality. One 

 is very near the P. bainbridgei pretiosa C. B. Ad. The other is the 

 ordinaiy type of this species and is similar to those forms found in. 

 the immediate vicinity of Mandeville. They are stated to be extinct 

 at Mt. Diabolo and are described as "semi-fossil." That they are 

 really extinct, however, would require an examination for young of 

 the species at the locality, as living adults of this species were not 

 seen during the time of my visit at any of the localities in the Mande- 

 ville region considered below, while young shells in very fresh condition 

 were found where the adult empty shells taken were all as weather- 

 worn as either of these two Mt. Diabolo specimens. The two Mt. 

 Diabolo specimens differ in many particulars, but as they came from 

 the sides of the road that crosses the hill they very likely are from 

 different colonies. As Mt. Diabolo is on the water shed dividing 

 the island into north and south portions, it is quite possible that these 

 two types represent a northern-side and a southern-side race. This 

 is rendered still more probable by the variations in the Mandeville 

 district specimens studied, w T hich seem to indicate two races that, 

 in some parts, have intermingled. 



The P. b. pretiosa type from Mt. Diabolo measures 30 mm. in height 

 by 55.5 mm. in width, with an index of .54, which is considerably lower 

 than many shells of this type that I collected in the Mandeville dis- 

 trict. The shell consists of 5 J whorls; on the last half of the last 

 whorl the suture is strongly impressed and the periphery is slightly 



