1901.] AFFINITIES OF UDENODON. 175 



middle. The 1st phalanx is a quadrangular bone slightly broader 

 than long and only slightly constricted in the middle. The 2nd 

 phalanx is a small bone very distinctly broader than it is long. 

 It gives articulation to a large claw. The terminal or ungual 

 phalanx is narrow, slightly curved, and almost as long as the meta- 

 carpal and the other two phalanges together. 



The fifth digit has a small metacarpal, about as broad as long, 

 and but slightly narrowed in the middle. The 1st and 2nd 

 phalanges are both small quadrangular bones, the 1st being 

 considerably smaller than the metacarpal, and the 2nd than the 1st. 

 The ungual phalanx is almost as huge as that of the fourth 

 digit, and like it but slightly curved. 



In Udenodon baini the metacarpals and phalanges appear to be 

 very like those in U. gracilis, but the ungual phalanges are much 

 shorter and broader, and the whole digits appear proportionally 

 stronger. 



Pelvis. 



In the skeleton of Udenodon gracilis ( Plate XVI. and Plate 

 XYIT. fig. 6) the almost perfect ilium (il.) is displayed. On the 

 right side the ischium (is.) and pubis (ph.), with a portion of the 

 ilium, are shown attached to the main slab, while the greater 

 portion of the right ilium remains adherent to the counter slab. 



The ilium resembles considerably the ilium of Ptychosiagum 

 orientate figured by Lydekker (7) in being directed upwards and 

 forwards, and in being greatly expanded antero-posteriorly. As 

 the acetabulum (ac.) is fairly large, the lower end of the ilium 

 which articulates with the pubis aud ischium is broad. On passing 

 upwards it becomes somewhat constricted into a short neck, from 

 which it again rapidly broadens into a large fan-like expansion. 

 The anterior part of the blade of the ilium lies much in advance of 

 the axis formed by the neck and the acetabulum, the anterior border 

 of the bone forming a graceful gentle curve forwards. The posterior 

 part of the blade is of much less size, and the posterior border 

 curves almost abruptly backwards from the neck and at right angles 

 to its axis. The iliac blades are moderately flat, being only slightly 

 concave antero-posteriorly on their outer side and with some 

 muscular ridges. 



The pubis (ph.) is peculiarly twisted, so that while the upper part 

 looks outward the lower looks mainly downward. The pubis forms 

 a little more than a quarter of the acetabulum, and bounds the 

 articular cavity by a prominent ridge. The outward facing portion 

 of the pubis is triangular in shape. In frout of the acetabulum 

 is a little prominence — apparently the pectineal tubercle; while at 

 the lower and anterior angle of the triangular portion is another 

 small tubercle, which iii position corresponds with the tubercle 

 which in Ornithorhynckiu assists in the articulation of the marsupial 

 bone. .\ ridge runs obliquely from this lower tubercle towards the 

 Lower border of the acetabulum, and from it the pubis passes at. 



tir«1 directly inwards ami then downwards and inwards. The 

 exact size <>l the obturator foramen (/."/..) is not elearlv shown 



