PHILOSOPHICAL SOCIETY OP WASHINGTON. 181 



Mr. Powell referred to the mound as being a burial-place for 

 many generations, and the large number of remains in any of 

 them as not indicating a large contemporaneous population. He 

 also spoke of the Pueblos as moving southward to newer, larger, 

 and better structures, and that those abandoned should not be 

 regarded as indications of extermination. 



Remarks were also made by Mr. White and Mr. Alvord. 



133d Meeting. December 22, isn. 



Vice-President Taylor in the Chair. 



Thirty-four members and visitors present. 



The election of Dr. David Lowe Huntingdon, U. S. A., and 

 Mr. Henry Robinson Searle, as members of the Society, was 

 announced. 



Mr. C. A. White made a communication on 



SOME PHASES OF THE EVOLUTIONAL HISTORY OF THE NORTH 

 AMERICAN UNIONIDiB. 



Remarks were made by Mr. Gill; Mr. Antisell, who objected 

 to the idea of propagation from salt to fresh water; Mr. Gilbert, 

 on the accommodation of fresh- water types to brackish water, 

 instancing fresh-water shells in the brackish water about Great 

 Salt Lake ; and by Mr. Gill, who referred to the existence of 

 sharks and other salt-water fishes in the fresh water of Lake 

 Nicaragua. 



Mr. Asaph Hall read a paper on 



THE POSITION OF THE CENTRE OF GRAVITY OF THE APPARENT DISK 

 OF A PLANET, 



giving the method he adopted in measuring the distances of the 

 satellites of Mars from the limbs of the primary, and reducing 

 them to the centre. 



{This paper appears in the Monthly Notices of the Royal Astronomical 

 Society for January, 1878.) 



