148 PROCEEDINGS OF THE ACADEMY OF [1890. 



April 1. 

 Mr. Thomas Meehan, Vice-President, in the chair. 

 One hundred and twelve persons present. 



The deaths of John Jordan Jr. and Frederick Graff, members, 

 were announced. 



Mr. Theo. D. Rand gave before the ]Mineralogical and Geological 

 Section the substance of his paper on " The Serpentines of South- 

 eastern Pennsylvania, " with lantern illustrations. 



April 8. 

 Mr. Gavin W. Hart in the chair. 

 Seveliteen persons present. 



April 15. 



The President, Dr. Joseph Leidy, in the chair. 



Twenty-nine persons present. 



Variatio7is in Bidimus exilis. — Dr. Benjamin Sharp called 

 attention to two varieties of Bnlimus exilis which he had found on 

 the islands of Guadeloupe and Dominica. One variety was charac- 

 terized by broad dark brown bands, which run parallel with the 

 coil of the shell ; while the other was peculiar in possessing small 

 and very faint bands, which in many specimens were entirely absent. 

 The banded variety was found to be common in Guadeloupe, while 

 the bandless one was rare. In Dominica, which is separated from 

 Guadeloupe by a channel of only twenty-three miles, the banded 

 variety was very rare, while the light or loandless one was compara- 

 tively common, although individuals were by no means so common 

 in Dominica as in Guadeloupe. He spoke of the probable cause 

 of the variation and suggested that it was due to some environ- 

 mental action. The island of Dominica being wholly of volcanic 

 origin, w^ould produce a different kind of food from the Grande 

 Terre portion of Guadeloupe, which in formation is purely coral. 

 It was on this portion of Guadeloupe that the specimens of B. 

 exilis were collected. It is known that Dominica has mauy species 

 and some genera of plants that are peculiar to the island, and this 

 difference of food may in some way account for the differences in 

 this species of land snail. Dr. Sharp said that it is probable that 

 the dearth of laud shells on the volcanic islands and their corapara- 



