334 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
Before proceeding farther, the writer desires to express his indebted- 
ness to Professor Scott for permission to study this important group and 
for much helpful criticism and encouragement during the progress of the 
work. A number of photographs of type specimens in the Ameghino col- 
lection taken by Professor Scott have proved of great value in the study 
of the diprotodont forms. Indeed, without their help, it would have been 
impossible to be at all certain regarding the determination of many of the 
species. The American Museum collection of Santa Cruz marsupials, 
especially rich in diprotodonts, was placed at the writer’s disposal by 
Professor H. F. Osborn, who has also contributed much valuable informa- 
tion regarding marsupial characters in general. Several important sug- 
gestions by Dr. W. D. Matthew and Mr. Charles Knight have been 
incorporated in the drawings of the restored skeletons of Prothylacynus , 
Borltycena and Cladosictis (PI. LXI). Dr. J. A. Allen has kindly per- 
mitted the examination and illustration of a skull of Ccenolestes obscurus 
in the collection of the American Museum of Natural History (PI. 
LXIII, figs. 14-14$). To Dr. Oldfield Thomas, of the British Museum, 
the writer is indebted for the loan of valuable osteological material illus- 
trating the skeleton of Thy lacy nus, without which it would have been im- 
possible to work out in a satisfactory manner the relationships of the 
Santa Cruz carnivorous marsupials. Liberal use has been made of this 
material in the figures presented in the accompanying text and plate 
(PI. LXV, figs. 1-1$). 
CLASSIFICATION OF THE SANTA CRUZ MARSUPIALS. 
As among recent marsupials, two suborders may be recognized, agree- 
ing in every respect with the Polyprotodontia and Diprotodontia. It has 
seemed advisable to retain the major subdivision of the order based on 
dental characters rather than to follow the recent classification proposed 
by Bensley (1903) in which dental characters are subordinated to foot 
structure, because practically nothing is known of the feet in the Santa 
Cruz diprotodonts, and what little is known of the feet in Ccenolestes , their 
nearest living ally, adds to the confusion already existing in the classifi- 
cation of the Marsupials by combining a non-syndactylous foot with a 
diprotodont dentition. 
The Santa Cruz representatives of the Polyprotodontia are carnivorous, 
