487 



rufus are closely repeated, with the difference of size and slight increase of breadth over 

 length, as in the sacrum ; and these permit an inference that the tail in Palorchestes 

 corresponded in strength, if not quite in relative length, to that in Macropus. 



§ 2. PalorchestesX (Os innominatum). — The pelvis of the Kangaroo is characterized 

 by a long prismatic ilium, an oblong tuberosity above or anterior to the acetabulum, a 

 " pectineal " or " ileo-pubic " process, the articular surfaces for the marsupial bones, 

 the broad, compressed, subprismatic form of the ischium, the slenderness of the pubis, 

 and the great length of both those elements of the pelvic arch. 



The length of the pelvis due to the great extension of the os innominatum both in 

 front and behind the acetabulum is a well-marked feature of resemblance to the same 

 part of the skeleton in the Bird, and similarly relates to the faculty of station and pro- 

 gression on the hind pair of limbs — the movement being, in the Kangaroo, as in some 

 tribes of birds, by a series of hops, the fore limbs, however, in the mammal taking also 

 an occasional share in progression on land, which is not permitted to the volant 

 class. 



The portion of pelvis (Plate CXXX.) corresponding in size with the sacrum (Plate 

 CXXIX.), although reduced to the parts immediately surrounding the acetabulum, 

 includes the base of the ilium, showing its three-sided prismatic form, the precotylar 

 tuberosity, and, above all, the " pectineal process " (ib. e), in size, shape, and position 

 closely corresponding with that in Macropus rufus (Plate LXXI. fig. 1, e, e). 



The anterior or haemal facet of the ilium (Plate CXXX. fig. 1, 62) is more deeply- 

 excavated than in the recent Kangaroo ; the rounded angle (a) dividing that facet from 

 the inner or median facet (ib. fig. 2, 62-) is relatively thicker. The precotylar tuberosity 

 (d) is more prominent, is relatively nearer the acetabulum ; and a ridge is continued 

 from the fore part of the tuberosity to the brim of that cavity, which more definitely 

 or abruptly there defines the haemal from the neural facets of the ilium than in recent 

 Kangaroos. 



The contour of the acetabulum is more ovate, the smaller end, at the fore part of the 

 brim, being narrower in the larger fossil. The notch (y) at the hind part of the brim 

 is narrower, and is nearly bridged over by the extension of the ischial (63*) toward the 

 pubic (u*) border of the notch; the depression (x) into which the notch expands at 

 the bottom of the cup is relatively narrower in Palorchestes than in Macropus. 



These characters would have indicated specific distinction if the present fossil had 

 not exceeded in size the corresponding part in the largest living Kangaroos ; the degree 

 to which Palorchestes surpassed them is exemplified in the pelvis as in the skull. 



Admeasurements of Pelvis. 



Palorchestes. Macropus rvfus. 



Breadth of haemal surface of ilium above the precotylar in. lines. in. lines. 



tuberosity 3 10 



Breadth of neural surface of ilium above the precotylar 



tuberosity 33 13 



