52 [March, 



throughout the country, thus establishing its electrical character beyond ques- 

 tion. Several persons have said that during the sanne time they distinctly heard 

 a snapping and cracking noise like that made by an electrical machine when in a 

 powerfully excited condition. This, however, may need confirmation. The 

 photometric power of the aurora when most brilliant, was about equal to that of 

 the moon in a very clear sky, when about three days old. ]No means were had 

 by the writer of examining the magnetic changes and disturbances. These, 

 however, have been probably carefully noted by accurate observers. From all 

 the phenomena noticed, however, the conclusion is a fair one that this aurora 

 was caused by a highly disturbed condition of the electrical tension of the air, 

 owing principally to calorific causes, and that however high it might have ex- 

 tended into the atmosphere, it undoubtedly rested upon the earth, and that in our 

 immediate vicinity. 



Dr. Leidy called the attention of the members to a specimen of the body of a 

 cervical vertebra, from the Eocene formation of Ouachita, Louisiana, belonging 

 to the cabinet of the Academy. It is perfectly mineralized, and both epiphyses 

 are attached, but portions are broken away, permitting the characteristic tuber- 

 culated surface of the body to be seen. It very probably belonged to a cetacean 

 animal, and is remarkable on account of the relatively deep concavity of its sur- 

 faces before and behind. For the animal to which the vertebra belonged, the 

 name Pontogeneus priscus was proposed. 



Dr. Leidy further made some remarks upon the comparative osteology and 

 dentition of the Hippopotamus, and proposed to consider the small species, 

 H. Libeiiensis, Morton, as belonging to a new genus of Hippopotamidae, under 

 the name of Chcerodes. 



Mr. Lea called attention to a specimen of Dipsas plicatus, Leachy 

 which was very remarkable for its size. It was a single valve, and 

 measured in length 6f inches, and in breadth 10 J inches. Its weight 

 was IO5 ounces. The heaviest specimen of a Vnio known to Mr. Lea 

 weighed two pounds ten ounces. 



Mr. Lea also exhibited some specimens of Uniones, which were appa- 

 rently hybrid, but in reality not so, the discrepancy arising from acci- 

 dental causes. 



March dth. 

 Mr. Isaac Lea in the Chair. 



Dr. Charles M. Wetherill read a paper intended for publication in the 

 Proceediiigs, entitled " Examination of Molybdate of Lead from the 

 Wheatley Mine near Phcenixville, Pennsylvania,^' which was referred to 

 Mr. Ashmead, Mr. A^aux and Dr. Eand. 



Mr. Lea read a "Description of a new species of SymphynoteUnio," 

 which being intended for publication, was referred to Dr. Leidy, Dr. 

 Iluschenberger and Dr. Bridges. 



A letter was read from Araory Edwards, Esq., dated New York, 

 March 3d, 1852, accompanying the donation of the heads of two 

 Gentoo Indians received this evening, of which the following is an ex- 

 tract : 



*The Gentoo tribe of Indians inhabit the sources of the Purus river, a South- 

 ern tributary of the Amazon. The marshy banks of this river render it so very 

 unhealthy that very little is known of its inhabitants. At intervals a half-breed 



