484 MR. A. H. G. DORAN ON THE MORPHOLOGY 



is hardly ever one third the size. The body of the incus of P. vulpina is well developed 

 and not much encroached upon by the articular surface, which has well-defined edges. 

 The processus brevis is stout and blunt-pointed ; it diverges little from the body. The 

 processus longus is long, rather straight and divergent ; it bears a small pedunculated 

 Sylvian apophysis. 



The stapes in large well-formed skulls of this species has a small aperture as in 

 Macropus ; its base is much longer horizontally than vertically ; and there is a small umbo 

 on the centre of the base. 



In Phalangista cookii the distinctive characters above given are still better marked. 

 The upper part of the head is well developed in the malleus, projecting well backwards 

 over the articular facets. The lamina is very narrow, but produced on to the processus 

 gracilis ; they together form a curved ribbon-like process of very even breadth through- 

 out. The incus is as large and well-developed a bone as in P. vulpina. The stapes 

 (PL LXIV. fig. 21) is most remarkable for a character already noted by Hyrtl (I. c.) : the 

 crura are united throughout without a trace of any aperture, forming a stout pillar, much 

 shorter than in any other Marsupial ; and the base is inflated into a large bulla projecting 

 prominently into the vestibule. I have not found this peculiar feature in any other 

 Phalanger ; and since Hyrtl represents it precisely as it appears in a specimen recently 

 procured from a Cook's Phalanger preserved in spirit in the store-room of the College 

 of Surgeons, it may be concluded that the bulla is a constant feature in this species. 

 Its morphological value does not appear to be great, as a bullate stapes occurs spo- 

 radically, so to speak, among higher mammals — for instance, in animals not closely allied 

 to each other, such as Mustela, Geomys, and Hyrax. 



In Petaurus (PL LXIV. fig. 22) the malleus has even still more pronounced features 

 than in Phalangista cookii. The head is markedly of the form already described in 

 Phalangista vulpina ; the neck is shorter, and the lamina rather wider ; but in the 

 riving Phalanger the manubrium is of stouter make in the above-described species, and 

 in the larger species (as in the fine and typical malleus of the Taguan, Petaurus 

 taguanoides, PL LXIV. fig. 23) it ends in a very marked spatulate dilatation *. 



The incus of Petaurus is a large bone with similar characters to that of Phalangista. 

 The stapes often has a distinct perforation, though otherwise it is columelliform ; the 

 base is much wider horizontally than vertically. 



In the characters of the malleus and of the large incus, the Plying Phalangers show 

 certain affinities to the Sciuromorphic Rodents. 



In the Koala {Phascolarctos fuscus, PL LXIV. figs. 24, 34) the malleus does not 

 possess the distinctive features so well marked in other Phalangers. 



The head is very small and ill-developed, projecting little either upwards or backwards ; 

 it is not much flattened laterally ; the articular surface is rather wide ; and the upper 

 facet is planer but much larger than the lower. The neck is long, thin, and curved, the 

 lamina rather narrow ; and the processus gracilis forms with it a similar process to that 

 in Phalangista, but more prolonged. The manubrium presents a great peculiarity 



* This dilatation is marked in Phalangista cookii, though the end of the manubrium is almost styliform in 

 P. vulpina. 



