Dr. W. Kiikenthal on the Dentition of Mammals. 279 
darker markings on the costal margin close to the apex. ‘The 
head, thorax, and abdomen pale greyish brown. 
Iixpanse 475 inches. 
Hab. Mexico, near Durango city (Becker). 
A fine distinct species, allied to P. argentiferus, Walker. 
XLII.— Observations on the Dentition of Mammals *, 
By W. K&KENTHAL f. 
WE do not yet possess a satisfactory explanation of the tooth- 
change of Mammals, as was shown by M. Schlosserf only a 
‘ short time ago. 
The conjecture that both series of teeth have been derived 
from the Reptiles 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 Marsupials, is confined to one premolar. —Flower’s§ 
hypothesis, afterwards considerably expanded by Oldfield 
‘Thomas ||, that the milk-dentition represents a fresh acquisition 
on the part of the higher Mammals, and that the permanent 
series alone is the original one, could therefore be supported 
by many weighty reasons. From among the large number 
ot views which differ from this in more or less material points, 
I will here merely allude to that of Baume j, according to 
which both series of teeth have had merely a secondary origin. 
For Baume supposes that owing to the shortening of the jaws 
which set in in the course of the evolution of Mammals, the 
originally numerous and similar teeth could no longer find 
room in one series, 80 that a portion of them became displaced 
and were able to appear only later on, as the permanent 
dentition. 
* T intend to give a detailed exposition of the present investigations in 
the second volume of my ‘ Vergleichend-anatomischen und entwickelungs- 
geschichtlichen Untersuchungen an Waltieren’ (Denkschriften der 
mediz.-naturw. Gesellschaft in Jena, Bd. iii.). 
+ Translated from a separate impression from the ‘Anatomischer An- 
zeiger, vi. Jahrgang (1891), no. 15, pp. 564-370. 
{ M. Schlosser, “‘ Die Milchbezahnung der Siugetiere,” Biolog. Centrabl. 
1890. 
§ W. H. Flower, ‘On the development and succession of the Teeth in 
the Marsupialia,” Phil. Trans., 1867. 
|| O. Thomas, ‘On the homologies and succession of the Teeth in the 
Dasyuride, with 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 Entwickelungsgeschichte des Gebisses ”: 
Leipzig, 1882. 
