218 



;is m Marsupials and most Mammals, they vary in length, curvature, degree in which 

 the groove for the intercostal vessels and nerve is excavated, distinction of head and 

 tubercle, and relative position of the latter (Plate XXXV.). 



The longest specimen measures 2 feet 1 inch, following the convexity of its curve. 

 The tubercle is low, 3^ inches from the head ; the intercostal groove is shallow, and 

 chiefly defined by a ridge-like production of the posterior border at the upper fourth of 

 the rib, 3 or 4 inches in extent. Beyond this the rib loses thickness and gains breadth, 

 the latter dimension reaching to 1| inch about one-third from the broken end. 



Another specimen presents a greater degree of curvature. The tubercle is better 

 developed, has a more definite articular surface, extending upon the neck of the rib. 

 The broadest part of the rib (1 inch 9 lines) is at the upper third of the bone. This rib 

 had a more anterior position in the chest than the former; the extent preserved, follow- 

 ing the convexity of the curve, is 1 foot 6^ inches. 



A third specimen with head, tubercle, and intercostal groove well marked, is less 

 curved than the former, and is larger than either of the above described. A length 

 of 1 foot 4 inches is preserved. The fractured end is elliptic, 1 inch 9 lines in long 

 diameter, 1 inch in short diameter ; but the rib midway between the end and the 

 head attains a breadth of 2 inches. This has come from nearer the middle of the 

 chest. 



The only entire specimen is a posterior rib, with the tuberosity relatively small and 

 rough ; the head large, intercostal groove almost obsolete ; body of the rib straight 

 along its distal half, which gradually expands, with loss of thickness to a breadth of 2 

 inches 2 lines. The length of this rib, following the convex curve, is 1 foot 8 inches. 

 The lower extremity shows the roughened surface for the attachment of the costal 

 cartilage. 



The costal fragments yield little more than the character of size. The vertebral end 

 of one, which includes the tubercle, has a circumference below that part of 3| inches. 

 Another fragment has a circumference of 4^ inches ; a third fragment is nearly 6 inches 

 in circumference ; a fourth fragment shows a flatter shape. 



From the shortness of the costigerous vertebrae and the size of the ribs, their inter- 

 spaces must have been narrow. 



Assuming with much confidence that the dorso-lumbar series in Diprotodon included 

 nineteen vertebrae, I assign one more pair of ribs than in the Kangaroo, and reckon 

 fourteen pairs in the dorsal series (Plate XXXV.). 



§ 6. Scapula. — The scapula is represented in the Boydian collection of Diprotodont 

 remains by an almost entire specimen of that of the left side (Plate XXX.), and by 

 a fragment of the one of the right side. 



It is narrow in proportion to its length, and chiefly peculiar by the production of the 

 subspinal plate anteriorly (ib. a), whereby the usual proportions of the triangular mam- 

 malian scapula are reversed, the part answering to the base (ib. b) being the apex, and 



