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AMERICAN JOURNAL 



Meeting June 4th, 1868. 



Ten members present. 



Dr. Lea, Director, in the Chair. 



Donations to the Museum and Library were read. 



The following paper, intended for publication in the Journal, 

 was presented and referred to a committee : 



"Notices and Reviews of New Conchological Works." By 

 Geo. W. Try on, Jr. 



The Publication Committee announced the issue of the "Ame- 

 rican Journal of Conchology," Vol. iv. Part 1, and of the " Mo- 

 nograph of Terrestrial Mollusca," Parts 5 and 6. 



Meeting July 2d, 1868. 



Eight members present. 



Mr. Tryon, Vice-Director, in the Chair. 



Donations to the Museum and Library were read. 



The following papers were read and appropriately referred: 



"Description of a new species of the genus Latirus." By 

 Wm. Harper Pease. 



" Description of a new genus and eleven new species of Land 

 Shells inhabiting Polynesia." By Wm. Harper Pease. 



Mr. S. R. Roberts exhibited extremely large specimens of 

 Anodonta from Thorpe's Dam, in the vicinity of Philadelphia, 

 including a single specimen only (among many of other species) 

 of Anodonta Tryonii, Lea. 



Mr. Gabb called the attention of the Section to the variations 

 of type that take place in genera during successive geological 

 periods. He remarked that, where a genus attains a strong nu- 

 merical development of species in any one age, those species 

 belonging to other periods, especially those most removed from 

 the chronological centre of development, so to speak, are usually 

 more or less aberrant from the average typical form of the genus. 

 This variation is so marked that the experienced palaeontolo- 

 gist can often recognize the geological age of a group of fossils 

 by their " facies," as it is termed, — their general appearance. 

 " They look like " such or such a formation. Nor is this pecu- 

 liarity confined to the stratigraphical range of genera ; it applies 

 also to their geographical distribution, as every working natu- 

 ralist knows and practically admits constantly in his studies. 



