MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 5 



majority of polyprotodonts were confined to Australasia, only one family 

 of polyprotodonts being known elsewhere, the Didelphiidae or opossum 

 family of South and Central America. Under these conditions, it was 

 a matter of the greatest interest when a small marsupial, widely different 

 from the opossums, was discovered in South America. This animal, 

 now known by the generic name Canolestes, presented an apparent 

 combination of diprotodont and polyprotodont characters, having a 

 diprotodont dentition and an eleutherodactylous foot. Moreover, it 

 was found to be closely allied to certain extinct forms known from 

 fragmentary remains from the Tertiary of Patagonia, being clearly a 

 surviving member of a highly differentiated group detailed knowledge 

 of which promised to throw new light on problems connected with the 

 origin and dispersal of marsupials. These facts were evident from 

 examination of the few specimens, consisting merely of skulls and skins, 

 which for many years were the only ones available. Such specimens 

 had been obtained through aboriginal sources and the exact habitat 

 of the animal was unknown. 



In 1911, while making general collections in the mountains of western 

 Venezuela (Osgood, 1912), I had the good fortune to discover C&nolestes 

 living in dense forests at an altitude of about 8000 feet. As a result of 

 assiduous trapping, a total of eleven animals was captured and, despite 

 poor equipment for the care of anatomical material, two entire specimens 

 representing both sexes and two others with some parts mutilated were 

 preserved in formaldehyde and bichloride of mercury. In addition, 

 several dry skeletons and a small number of conventional skins and skulls 

 were saved. This material has formed the basis of the following study. 

 Its importance seemed to demand the fullest possible treatment and, 

 although this has not been accomplished, it is hoped that sufficiently 

 detailed information has been obtained to warrant general conclusions. 

 Study of particular organs and systems by specialists would have been 

 exceedingly desirable, but the nature of the material and the conditions 

 under which it has been studied have not made this feasible except to a 

 limited extent. 1 The cooperation of Dr. C. Judson Herrick has been 

 greatly appreciated and his description of the brain of Canolestes to- 

 gether with the figures drawn under his direction which are incorporated 

 in the present publication will doubtless add greatly to its value. 



Comparative material, especially of Australian forms, has been 

 confined almost exclusively to skeletons and skulls. Fortunately a fairly 

 representative collection of these is possessed by Field Museum and 

 this has been supplemented by specimens borrowed from the U. S. 



1 It is especially to be regretted that no study of the organ of Jacobson has been 

 made. 



