788 PBOF. BALDWIN SPENCER ON A [Nov. 20, 



in Trichosurus and other Phalangerinae it cuts across the same 

 angle. 



The measurements of the tibia and fibula are as follows : — Tibia, 

 length 99 mm.; greatest width of head 25 ; width at tuberosity 

 13. The comparative lengths of the tibia in the following species, 

 taking in each case the length of the skull as 100, are : — Tricho- 

 surus fuliginosus 118"4 ; Dasyurus maculatus 94*6; Pseudochirus 

 archeri 97'4 ; Sarcophilus ursinus 96 ; Bettongia penicillata 21S ; 

 Phascolarctos 82*6 ; Didelphys marsupialis 82*2 ; Phascolomys 

 mitchelli 65-2 ; Phalanger sp. 80'6. 



Fibula, length 99. Comparative length of the fibula in the 

 following species, taking in each the length of the skull as 100 : — 

 Trichosurus fuliginosus 115"4; Dasyurus maculatus 94*6; Pseudo- 

 chirus archeri 97*4 ; Sarcophilus ursinus 94 - 2 ; Bettongia penicillata 

 210"9 ; Phascolarctos 81*2 ; Didelphys marsupialis 71'5 ; Phasco- 

 lomys mitchelli 65-2 ; Phalanger sp. 80-6. 



It will be noticed that the nearest approach in relative length 

 of both tibia and fibula is met with in Pseudochirus, the next nearest 

 being Dasyurus and Sarcophilus. 



Pelvic Girdle, (Fig. 4, PL XLIX.) 



The parts of this remaining are the acetabular region and 

 ischium and the greater part of the ilium of the risht side. The 

 whole girdle is remarkable for its great massiveness. 



The ischial portion is somewhat similar to that of Trichosurus, 

 the border which lies on the internal side in the acetabular region 

 bending outwards and downwards to the tuber ischii, though it is 

 nothing like so sharply marked as it is in Trichosurus, in which it 

 forms a distinct ridge. The acetabular cavity is deeper than in 

 Trichosurus or Dasyurus, the two margins of the articulating 

 surface approaching more nearly one to the other inferiorly, owing 

 to the fact that the posterior margin which overhangs the cotyloid 

 notch faces somewhat more forwards than it does in the Phalan- 

 geridae or Dasyurida?. The cotyloid notch is deep, though not so 

 deep as in the Macropodidae. The synovial cavity is distinctly 

 outlined, but, except in the posterior part, is not overarched by the 

 acetabular border. Owen 1 laid some stress upon the presence of 

 this feature in Thylacoleo as being indicative of the alliance of the 

 latter with the carnivorous marsupials, but it is also present in 

 certain herbivorous forms. The shape of the acetabular region on 

 the whole more nearly resembles that of Phascolomys than of any 

 other form. 



The ilium is unfortunately somewhat broken along its postero- 

 internal or iliac border, but is sufficiently intact to show that it 

 does not closely resemble that of any existing marsupial. The 

 three surfaces — gluteal, iliac, and sacral — are sharply defined, and 



1 " Pelvic Characters of Thylacoleo carnifex " Pbil. Trans. E. S. part ii. 

 18S3. p. 639. 



