OF THE AUSTRALIAX MAESUPIALIA. 211 



Upper lateral incisors absent. ]\Iolars quadrituberculate, bunodont, 

 hypsodont, rootless. Pes of normal proportions. jNJesocuneiforni 



free; hallux vestigial Phascolomyid.e. 



Pes digitigrade; incisors trenchant. ^Median premolars developed as 

 sectorials in young. 



Incisor formula j. Molars rooted, bunodont, brachybuuodont and 



quadrituberculate, or lopbodont. Sectorial premolars grooved . Macropodid.k. 

 IncertcE sedls. Pes? Functional incisor formula -r. Incisors piercing. 

 Sectorial premolars excessively enlarged and smootli-cd;icd. Molars 

 vestigial or absent Thvlacoleontid.k. 



The writer takes this opportunity of expressing his indebtedness to ihe officers and 

 others of the Geological and Zoological Departments of the British Museum who 

 rendered him assistance during the preparation of the present paper, more esjjecially to 

 Dr. Henry Woodward, Dr. Smith Woodward, Mr. Oldfiekl Thomas, and Mr. Eichard 

 Lydekker. 



At an early stage of the work it was the intention to attempt to trace the sequence 

 of dental and particularly incisor reduction in the Marsupials by reference to embryonic 

 forms, and while this had ultimately to be abandoned for lack of time, the writer is 

 indebted to Professor G. B. Howes, of the Eoyal College of Science, for affording him 

 access to the laboratory and research material of that institution. He also wishes to 

 record the kindness and liberality with which the late Mr. Martin F. Woodward placed 

 his valuable private collection of foetal Marsupials at his disposal. 



Final acknowledgment is due to Professor Henry F. Osborn, of Columbia University, 

 New York, for friendly advice and supervision. 



Bibliography. 



1901. Allen, J. A. A preliminary Study of the North-American Opossums of the Genus Didelphis. 



Bull. Am. Mus. Nat. Hist. vol. xiv. art. 11, pp. 119-188. 

 i8gi. Ameghino, P. Nuevos restos de mamiferos fosiles decubicrtos per Carlos Ameghino en cl 



eoceno inferior de la Patagonia austral. Ilevista Argentina dc Ilistoria Natural, torn, i., Oct. 



1891, pp. 289-328. 

 1894. Bateson, W. Materials for the Study of Variation. 8vo. London. 

 1901a. Benslev, B. A. A Theory of the Origin and Evolution of the Australian Marsupialia. Am. 



Naturalist, vol. xxxv. no. 412, pp. 2 I.1-2G9. 

 i<^o\b. On the Question of an Arboreal Ancestry of the Marsupialia, and the Interrelationships 



of the Mammalian Subclasses. Am. Naturalist, vol. xxvv. no. 410, pp. 117-138. 

 1896. Broom, R. Beport on a Bone Breccia Deposit near the Wombeyan Caves, N.S.W. ; witli 



Descriptions of some new Species of JMarsupials. Proc. Linn. Soc. N.S.W., part 1, 



April 28th, pis. 6-8. 

 1898. On the Affinities and Habits of Thylacoleo. Proc. Linn. Soc. N.S.W., part 1, 



April 27th, pp. 57-7-1. 

 SECOND SERIES. — ZOOLOGY, VOL. IX. S9 



