some Ungual Phalanges. 315 



which the proximal articular surfaces, allowing for wear and 

 tear, arc perfect. The lateral surfaces (at the point of 

 disruption in PI. XIX. figs. 8 & 9) suddenly bulge outwards 

 to form an expanded proximal end with a concave articular 

 surface divided by a longitudinal central ridge, and below a 

 very strong and comparatively large cushion for the attach- 

 ment of the flexor tendon. Immediately above the centre 

 of the tendon tuberosity on either side, are the foramina of 

 the digital arteries. The surface of both specimens is pitted 

 and roughened. 



Length of complete bone 51 mm. ; breadth 45 mm. 

 approximately ; thickness 13 mm. 



Type 2. — The phalauges of the second type (Pis. XVIII.— 

 XIX. figs. 2-7) differ from those of the first by a greater 

 length in proportion to width, a much less arched dorsal edge, 

 and a slightly less lateral compression, otherwise the same 

 features characterize both. The following are the dimensions 

 of the largest : — 



Length 45 mm.; breadth 29 mm.; thickness 11 mm. 

 In the sheathed, or hooded terminals of Owen, although 

 the nail-bone is compressed laterally (PI. XVIII. fig. 1) the 

 dorsal edge is only sharp or trenchant distally, the proximal 

 end is truncate-flattened forming an elongately triangular 

 surface. The articular surface for union with the distal 

 end of the penultimate digit is highly concave, and much 

 overhung above, as figured both by Owen and Krefft. The 

 sheath is oue with the core, or nail-bone, at the proximal 

 end around the articular concavity, and along the plantar 

 surface as far as it extends; the tuberosity is to some extent 

 flattened. The arterial foramina pierce the sheath through 

 the plantar surface of the tendon tuberosity, and then 

 appear to enter the nail-bone as in the preceding type. 

 Immediately below the dorsal truncate surface at the proxi- 

 mal end are two other arterial foramina. 



Now, to what type of Marsupial do these ungual phalanges 

 (Pis. XVIII.-XX. figs. 2-12) belong? It will be more 

 satisfactory to consider T>pes 1 and 2 separately. Type 1 

 (Pis. XIX.-XX. figs. 8-12) is the " nail-bone of a gigantic 

 Piialanger of Krefft/ - ' but this form appears to have been 

 quite unknown to Owen. In the Macropodidse the nail- 

 bones are elongate, non-trenchant, more or less oval in 

 section, and very feebly arched, if at all. The nail-bones of 

 the Peramelidte are double, more or less circular, and non- 

 trenchant. In the Phascolomyidse, or Wombats, these 

 terminals are again rounded above, roughly oval in section, 

 and not hooked. The nail-bones of the Diprotodontidae, 



