natural sciences op philadelphia. 37 



April 2. 



Mi'.Vaux, Yice-President, in the chair. 



Twenty-three members present. 



The following paper was presented for publication : 



" Descriptions and Illustrations of Genera of Shells." By T. A. 

 Conrad. 



Remarks on some Extinct Mammals. Prof. Leidy exhibited 

 specimens of fossils from the Tertiary of Wyoming. One of these 

 is an upper jaw fragment with two molars ; the other a lower jaw 

 fragment with a single molar. The upper molars have crowns 

 composed of four lobes, of which the outer are like the corres- 

 ponding ones in Anchitherium. Of the inner lobes, the front one 

 is much the larger, and is prolonged outwardly in advance of the 

 antero-external lobe. It is homologous with the antero-internal 

 and antero-median lobes as existing in Anchitherium in a com- 

 pletely connate condition. The postero-internal lobe is the smallest 

 of the crown. It is conical and conjoins that in front. A barely 

 perceptible trace of a postero-median lobe is seen. A strong basal 

 ridge incloses the crown, except externally, where it is feebly 

 produced. 



The three upper molars occupied a space of 8 lines. The first 

 molar is 2^ lines fore and aft and 3^ transversely ; the second is 

 2| lines fore and aft, and the last one 2 lines. 



A question arises as to whether these teeth pertain to any of 

 the animals previously indicated from lower jaw specimens with 

 teeth. They are too large for the known species of Hyopsodus or 

 Microsyops. They nearly accord in size with the lower molars of 

 Notharctus, and perhaps belong to this genus. Linnotherium 

 appears not to differ from this, as the number of teeth and their 

 constitution are the same. 



The lower jaw fragment accompanying the upper one may be- 

 long to the same animal. The molar it contains, though resembling 

 those of Notharctus, differs in several points. I propose to refer 

 the fossils to a species with the name of Hipposyus formosus. 



Prof. Leidy further remarked that he had recently the oppor- 

 tunity of examining the tooth described by Prof. Marsh under the 

 name of Palseosyops minor. The tooth evidently belongs to the 

 curious pachyderm with the beaver-like incisors named Trogosus 

 castoridens. On observing the molar tooth, which is not worn away 

 like those in the jaw specimen upon which the latter was named, 

 it at once called to mind, the tooth which had been described 

 under the name of Anchippodus riparius. On comparison, it 

 would appear as if the specimens referred to Paleeosyops minor 

 1872.] 



