278 [October, 



Dr. Leidy exhibited three broken teeth, consisting of the body of a 

 canine and that of two posterior molars, which, he observed, were 

 fossils from Nebraska Territory, and belonged to an animal closely 

 allied to the genus Ursus. The tubercles upon the crown of the molars 

 are more elevated and conoidal than in the recent bears, and the 

 crown of the canine is relatively more robust. He proposed for the 

 animal the name of Arctodon. 



Dr. L. stated that he was preparing a memoir, in which would be 

 described in detail all the fossil remains of Mammalia from Nebraska 

 Territory, heretofore characterized by him in the Proceedings. 



He next presented for examination a species of fresh-water sponge 

 found growing in the Delaware and Schuylkill rivers, in the vicinity 

 of Philadelphia, which he characterized as follows: 



Spongilla fragilis. Discoidal, lichenoid, growing in patches, flat, oval or 

 circular, lobate at the margin, translucent, yellowish-white or cream-colored. 

 Areolae distinct, subcircular. Reproductive bodies arranged in a single close 

 layer at the base of attachment of the sponge, shining, whitish-yellow, elevated 

 into a central papilla upon the upper surface. 



Measurements. From i to 2 inches in diameter by 1 to U lines in thickness 

 at the centre and gradually thinning off to the margin. 



Hahitatioii. Grows upon the under side of stones below low water mark in 

 the Rivers Delaware and Schuylkill. 



Siructtire. Compesed of an intertexture of spiculae about l-400th of an inch 

 long, having a minutely tubeiculated surface, over which is reflected a granulo- 

 cellular membrane. 



Remarl-s. After the death of the sponge, the areolated tissue macerates off, 

 leaving the reproductive bodies in a close layer attached to the rock. The living 

 sponge is never green, nor does it ever grow exposed to the light. 



Dr. L. further stated that another species of fresh-water sponge is not un- 

 common in our rivers, which grows exposed to the light, and is green in color 

 like the European Spongilla fluviatilis, but whether it is specifically distinct 

 from the latter, he has not yet ascertained. 



October 2StJi. 

 Vice-President Wetherill in the Chair. 



The Committee to which was referred Mr. Lea's paper on the genus 

 Acostrea, of D'Orbigny, reported in favor of publication in the Journal. 



The Committee to which was referred Mr. Cassin's " Catalogue of 

 the Caprimulgidfe in the Collection of the Academy of Natural 

 Sciences of Philadelphia," reported in favour of publication. [D^^i'or 

 this paper see the end of the present number. ~] 



The Committee to which was referred the following paper of Mr. 

 C. Girard, reported in favor of publication in the Proceedings. 



