OF THE AUSTEALIAN MARSUPIALIA. 171 



NOTOEYCTIDtE. 



Apart from the original description by Stirling (1891), the chief observations on the 

 foot-structure of Notoryctes are those of Gadow (1892), Winge (1893), and Dollo (1899). 

 Of the last-named writers, Gadow and Dollo have made comparisons with other 

 Marsupials with conflicting results, tlie former finding resemblances to the Didelphyidse 

 and DasyuridfP, the latter to members of the syndactylous series, more especially the 

 Peramelidae. The following remarks are designed to show that the balance of evidence 

 is in favour of the latter view. 



It may be observed at the outset that the pes of Notorfjctes is so highly specialized 

 that the exact manner of derivation cannot be affirmed with certainty. 



The plantar surface shows no indications of arboreal pads, being covei-ed by a leathery 

 wrinkled skin. The hallux is well developed and possesses the full number of phalanges 

 as in the Phalangeridse and Didelphyidse. Its terminal phalanx is provided with a 

 flattened claw. In this respect Notoryctes is unique among the Marsupialia, Winge, 

 who follows Gadow's view as to the dasyurid affinity of the animal, suggests the 

 possibility that the hallucal claw is of secondary origin ; and this explanation is in all 

 probability the correct one — Notoryctes being highly specialized in other respects. The 

 entocuneiform bone is comparatively long. As pointed out by Owen, and by Dollo for 

 the present form, tliis character represents an arboreal adaptation. Gadow mentions 

 the presence of a prehallucal element attached to the entocuneiform as indicative of 

 affinity with Didelphys, in which it is also present. An examination of other genei*a 

 of Didelphyidte shows that the element is of fairly general occurrence in this family. 

 It is absent in the adults of all the Australian forms, but Emery has described it in 

 embryos of certain species. 



The hallucal articular facet of the entocuneiform is figured by Stirling as terminal 

 {cf. text-fig. 6, B, p. 172). In an exhibition skeleton in the B.M. Collection (text-fig. 6, C) 

 the terminal portion of the entocuneiform is wedge-shaped, the one side of the wedge being 

 applied to the proximal portion of the second metatarsal, while the other bears the 

 articular facet. The hallux thus occupies a position of partial opiiosability. This 

 condition is more apparent in one foot than in the other. A somewhat similar tendency 

 towards variation is found vinder the same conditions in Phascolomys. In Notoryctes 

 a formerly opposable hallux is apparently returning to an orthjil position while remaining 

 functional, while in Fhascolomys a formerly opposable hallux retains a more or less 

 opposable position, but is becoming vestigial. 



Gadow regards the second and third digits of Notoryctes as fi'ee as in " Didelphyidfe, 



Dasyurus, Thylacinus, Phascogale, 3Iyrniecobius, Fhascolomys There is at the utmost 



a very slight indication of syndactylism of the second and third toes, far less obvious 

 than it is even in Phascolomys." Dollo, on the otlier hand, recognizes a slight reduction 

 and syndactylism of these digits, as in the arboreal Phalangeridce. A spirit-specimen 

 {cf. PI. 7. fig. 19) examined by the writer shows very definite indications of syn- 

 dactylism. It is true that the condition is not so marked as in normal forms, because 



SECOND SERIES. — ZOOLOGY, VOL. IX. 24 



