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XXIII. On Hypsiprynmodon, Ramsay, a Genus indicative of a distinct Family (Pleopo- 

 didse) in the Diprotodont Section of the Marsupialia. By Prof. Owen, C.B., 

 F.B.S., F.L.S., Sfc, Superintendent of the Natural-History Departments in the 

 British Museum. 



(Plates LXXI. & LXXII.) 



Read January 17th, 1878. 



_L HE modification of the hind foot in the Marsupial series is peculiar in the way in. 

 which the digits depart from the typical mammalian number, 5. The peculiarity is 

 chiefly shown by an atrophy of the second and third digits of a kind like that which 

 affects the third digit of tbe fore foot in the Aye-aye — namely, attenuation without loss 

 of length, and this in relation to a special use distinct and apart from the foot as a loco- 

 motive or prehensile organ. 



Not only are the slender metapodials of the digits n and in (PL LXXII. fig.. 10) wrapped 

 up with the others in a common sheath of skin, but also the proximal and middle 

 phalanges, leaving only the distal ones with their claws free, but in close contact and of 

 equal length ; and these claws have been uniformly observed in the Marsupials with 

 the so-modified hind foot to be used as scratchers and cleansers of the fur. 



This condition of hind foot is found in carnivorous, frugivorous, and herbivorous Mar- 

 supials, and is associated with as many distinct formulae of the dental system. 



The modification of digits n and in, moreover, may coexist with the normal develop- 

 ment of the digits rv and v, and with an abnormal one of digit i, in the form of a 

 powerful opposing hallux, as exemplified in the grasping hind foot of the scansorial 

 phalangers (woodcut,, fig. 1) ; or it may be associated with an abnormal development of 

 the digits iv and v in both breadth and length, especially of iv, with a reduction of 

 digit i to rudimental insignificance, as in the gradatorial Bandicoots (Ferameles) ; or it 

 may be associated with a still greater development of digits iv and v, and especially of 

 rv, with total loss of digit I, as in the hind foot of the saltatorial Potoroos and Kan- 

 garoos (woodcut, fig. 2). 



But in the subject of the present paper a completely developed hallux (wOodcut, fig. 3 3 

 PL LXXII. fig. 7, i) is combined with the fur-cleansing and locomotive toes of the 

 Poephaga* ; and this singular osculant condition of foot is associated with the dentition of 

 the Sypsiprymnidce. Thus the transitional character of the mammal under consideration 

 would seem to place the genus between the scansorial and saltatorial groups of the great 

 diprotodont division t of the Marsupial order. The analogous approach in digits u and 

 in to the Kangaroo type of foot made by the Bandicoots (Feramelidce) may be a mere 

 adaptive one in relation to their fur, and at any rate is an affair of one of the Polypro- 



* "-Outlines of a Classification of the Marsupialia," Trans. Zool. Soc. vol. ii. 1839, p. 332. 

 ■f ' Researches on the Fossil Remains of the Extinct Mammals of Australia,' 4to, 1876, vol. i. pp. xii, 107. 

 SECOND SERIES. — ZOOLOGV, VOL. I. 4 G 



