Dr. W. Kiikciitlial on the Dentition of Mdinmah. 270 



clavkcr markings on tlie costal margin close to the aj)ex. 'J'lic 

 head, thorax, and abdomen pale greyish brown. 



Expanse 4x"o inches. 



Hah. Mexico, near Dnrango city [Becker). 



A fine distinct sjiceies, allied to P. argentiferini, Walker. 



XLIII. — Observations on tlie Dentition of ManiraaJs'^ . 

 \\y W. KiJKENTHAL t- 



We do not yet possess a satisfactory explanation of the tooth- 

 change of Mammals, as was shown by M. Sclilosserf only a 

 short time ago. 



The coiijcctnre that both series of teeth have been derived 

 from the Keptiles is at once opposed by a number of state- 

 ments, according to which in the lower orders of Mammals 

 tooth-change is either entirely absent, or, as in the case of 

 the ]Marsu})ials, is confined to one premolar. Flower's § 

 hy})Othesis, afterwards considerably expanded by Oldfield 

 'i honias |i, that the milk-dentition represents a fresh acquisition 

 on the ])art of the higher ]\Iannnals, and that the permanent 

 scries alone is the origiinil one, could therefore be supported 

 by many weighty reasons. From among the large number 

 of views which differ from this in more or less material points, 

 1 will here merely allude to that of Baume^, according to 

 w hieh both series of teeth have had merely a secondar}^ origin. 

 For Baume sujiposes that owing to the shortening of the jaws 

 which set in in the course of the evolution of Mannnals, the 

 originally numerous and similar teeth could no longer find 

 room in one series, so that a portion of them became displaced 

 and were able to appear only later on, as the permanent 

 dentition. 



* I intend to give a detailed exposition of the present investigations in 

 the second volume of my ' ^'erg•Ieic•hend-anatOIniscllen und entwickelunjis- 

 gesehichtlicheu Untersuchungen an Waltieren ' ( Denkschriften der 

 mediz.-naturw. Gesellschaft in Jena, Ikl. iii.). 



t Translated from a Separate impression from the ' Anatomischer An- 

 zeiger,' vi. Jahrgang (1891), no. 13, pp. 364-370. 



\ M. Schlosser, " Die Milchbezahuuno-derSaii2etiere,"Biolog. Centrabl 

 1890. 



. § W. II. Flower, '"On the development and succession of the Teeth in 

 the Marsupialia,'' Phil. Trans., 18()7. 



II O. Thomas, " On the homologies and succession of the Teeth in the 

 Dasyuridre, witli an attempt to trace the history of the evolution of the 

 Mammalian Teeth in general, ' Phil. Trans, vol. 178, pp. 443-462. 



% Baume, " Versuch einer Ilntwickelungsgeschichte des Gebisses": 

 Leipzig, 1882. 



