1851.) 2Gi 



September 2(1, 1851. 

 Vice President Bridges in the Chair, 



A letter was read from the Trustees of the New York State Library, 

 dated Albany, August 1 1th, 1851, acknowledging the receipt of late 

 numbers of the Proceedings. 



Also a letter from Mrs. Charlotte K. Townsend, dated Philadelphia, 

 1851, returning her acknowledgments for certain resolutions recently 

 adopted by the Academy. 



Mr. Lea remarked that he had observed in a recent number of the Proceedings 

 of the Boston Society of Natural History, a communication on the subject of the 

 " Wave Theory," in regard to the dynamics of earthquakes. He observed that 

 this " wave theory" was by no means of as recent a date as was generally ima- 

 gined, and stated that Dr. Franklin, while in France in 1782, distinctly suggested 

 this wave motion, produced by a central force reaching to an immense distance. 

 Mr. L. read part of Dr. Franklin's letter to the Abbe Soulavie, (Trans. Am. 

 Phil. Soc, Vol. 3, p. 1, old series,) dated at Passey, September 22d, 1782, in 

 which he says, " But we are still subject to the accidents on the surface, which 

 are occasioned by a wave in the internal ponderous fluid : and such a wave is pro- 

 ducible by the sudden violent explosion you mention, happening from the junction 

 of fire and water under the earth, which not only lifts the incumbent earth which 

 is over the explosion, but impressing with the same force the fluid under it, 

 creates a wave that may run a thousand leagues, lifting thereby successively 

 all the countries under which it passes." 



September 9th. 

 Vice President Bridges in the Chair. 



A communication was read from Aug. A. Gould, M. D., and D. 

 Humphreys Storer, M. D., Executors of the late Thomas Binney, M. D., 

 of Boston, dated Boston, July, 1851, presenting, in accordance with 

 his will, a copy of Vols. 1 and 2 of his work on the Terrestrial Mol- 

 lusks of the United States. 



Dr. Leidy called the attention of members to a fragment of rock a 

 few inches square, covered upon one surface with numerous root-like 

 fibres, which he stated belonged to a species of branching, fresh water, 

 ciliated polyps of the genus Plumatella. The piece had been broken 

 from a slab 18 inches square, which was entirely covered upon its 

 under surface in the same manner. The species he characterized as 

 follows : 



PLUMATELLA, Bosc. 



Plumatella diffusa, n. s. 



F olypidom, diverging from a centre over large surfaces, consisting of a series 

 of simple curved branches, from one to two lines long, rising from one another 

 upon the convex side, and attached throughout their length except at the extremi- 

 ties for l-4th to 2-5ths of a line, which are erect, keg-shaped, or a little dilated 

 at the middle and contracted at the orifices. Border of the orifices deeply emar- 



TROCEED. ACAD. NAT. SCT. OF PHILADELPHT A . VOL. V. NO. XI. 3t 



