110 
JOURNAL OF MAMMALOGY 
B, Heritage 
Accepting the views of Huxley, Dollo, Bensley, Osgood and others 
that the existing Didelphidse stand near the center of the adaptive 
radiation of the marsupials (a view endorsed by Matthew, 1913, on 
palaeontological grounds) we find that in its nutritional habitus Ccenolestes 
is almost intermediate between the primitive insectivorous polypro- 
todonts and the more primitive Australian diprotodonts, such as 
Distoechurus of the Phalangeridae. Thus in the dentition it inherits 
from the polyprotodonts the primitive dental formula, the tuberculo- 
sectorial character of the lower molars, the remnants of trituberculy in 
the upper molars, and of the external cingula in both the upper and 
the lower molars. On the other hand Ccenolestes has advanced in the 
direction of the diprotodonts in acquiring fully developed diprotodonty 
of the front teeth, and a remarkably kangaroo-like papilla incisiva, 
while the upper and lower molars approach the pattern of those of 
the smaller phalangers. But neither in Ccenolestes nor in any of its 
known extinct relatives is the dentition as a whole sufficiently close to 
those of Australian diprotodonts to warrant us in referring them to any 
given Australian family. In comparison with that of PerameleSj the 
dentition of Ccenolestes differs radically; for the former may best be de- 
rived as by Bensley (Pis. 5, 6) from some small polyprotodont, such as 
Peratherium, with inwardly grown para- and metacones and heavily 
developed buccal stylar cusps. In the Peramelidse the dentition, while 
remaining polyprotodont in front, has become hyposodont in the cheek 
teeth, while Ccenolestes has acquired diprotodonty in the front teeth 
and incipient lophodonty in the cheek teeth. In brief, as regards its 
dentition, Ccenolestes and the whole family of Palseothentidse may rep- 
resent an independent group not directly ancestral to any Australian 
diprotodont, but lying between the Peramelidse and the Phalangeridae, 
as suggested by Osgood. 
In respect of the organs used in detecting the food, Ccenolestes may 
well represent a secondary specialization in the excessive size of its 
olfactory, tactile and auditory organs and in the reduction of the sense 
of sight which is fairly well developed in the smaller Didelphidae. 
With regard to the stomach, which is peculiarly specialized, Osgood 
remarks (p. 72) that this organ is unique and serves to strengthen the 
general conclusion that the animal stands by itself quite as independ- 
ently as any of the highly specialized Australian forms. Osgood also 
remarks (p. 78) that the short colon combined with the small caecum 
in Ccenolestes is contrary to the usual condition in marsupials and is 
