o2 [ MARCH, 
throughout the country, thus establishing its electrical character beyond ques- 
tion. Several persons have said that during the same 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 ina 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. Liberiensis, Morton, as belonging to a new genus of Hippopotamide, under 
the name of Cherodes. 
Mr. Lea. called attention to a specimen of Dipsas plicatus, Leach, 
which was very remarkable for its size. It was a single valve, and 
measured in length 6? inches, and in breadth 103 inches. Its weight 
was 103 ounces. The heaviest specimen of a Unio 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 9th. 
Mr. Isaac Lea in the Chair. 
Dr. Charles M. Wetherill read a paper intended for publication in the 
Proceedings, entitled ‘‘ Examination of Molybdate of Lead from the 
Wheatley Mine near Phoenixville, Pennsylvania,” which was referred to 
Mr. Ashmead, Mr. Vaux and Dr. Rand. 
Mr. Lea read a ‘‘ Description of a new species of Symphynote Unio,” 
which being intended for publication, was referred to Dr. Leidy, Dr. 
Ruschenberger and Dr. Bridges. 
A letter was read from Amory 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 
