172 proceedings of the academy of [1892. 



April 5. 

 Mr. Thomas Meehan, Vice-President, in the chair. 

 Fifty-three persons present. 



April 12. 

 The President, General Isaac J. Wistar, in the chair. 

 Forty-five persons present. 



April 19. 

 The President, General Isaac J. Wistar, in the chair. 

 Thirty-one persons present. 



April 26. 



The President, General Isaac J. Wistar, in the chair. 



Sixty-five persons present. 



A paper entitled "On the Mechanical Genesis of the Scales of 

 Fishes," by John A. Ryder, Avas presented for publication. 

 Prof. F. H. Giddings was elected a member. 



On the Molars of the Pteropine Bats.—T>R. Harrison A.llen 

 called attention to the homologies of the cusps of the molars in the 

 ptero|)ine bats. In Pteropus medius the grinding surface of the 

 parallelogram-like crown of the first upper molar is traversed its 

 entire length by a groove which is bounded externally by a thick 

 ridge and internally by a narrow ridge. The outer ridge forms an 

 imperfectly developed cusp at its anterior part which is probably the 

 paracone. The inner ridge is imperfectly divided into two sub- 

 equal parts, of which the anterior is probably the protoconeand the 

 posterior the metacone, the heel (hypocone) being absent. These 

 identifications agree with the cusps as seen in other mammals. 

 Owing to the great size of the grinding surface it becomes difficult 

 to understand why the backward extension of the tooth differs from 

 other types in the form of the primary cusps instead of the evolu- 

 tion occurring as is the rule by the appearance of the hypocone. 



The commissure which constitutes the anterior and the posterior 

 borders of the tooth are exceptionally well defined and the one last 



