28 ON BONES AND TEETH OF EXTINCT LIZARD, 
in the living genera. The proximal edge of the articulating 
surfaces of the joint on this aspect is nearly parallel with their 
distal edge—in Hydrosaurus and Odatria it slopes rapidly from 
the radial condyle inward; in Monitor there is more approxi- 
mation to its direction in the fossil. 
On the dorsal side the surface of the distal expansion is 
strongly convex—above the middle of the mesial line of the 
shaft is the broad shallow pit for the powerful tendon of the 
latissimus dorsi (Pl. 2, 1.d.) and on the inner side of it and 
below it a low ridge passes down, curving outwards in its 
course to reach the mesial line. The anterior (outer) edge of 
the shaft ascends with a strong concave sweep to the deltoid 
insertion (PI. 2, del.), which stands ont prominently: and the 
contour of this side of the bone clearly indicates an expansion 
of the proximal in just proportion to that of the distal end. 
On separating from the foregoing statement of the superficial 
characters of the fossil those from which its nearest affinities 
may be deduced it is not easy to derive a definite opinion from 
them alone—the relations of Notiosaurus seem to librate equally 
between Hydrosaurus and Monitor; but when we take into 
account the comparative dilatation of the bone in Monitor this 
of surviving genera appears to have diverged the least from its 
predecessor. 
Lerr scapota.—(Puare III.) 
In the Australian genera of the Monitor group of lizards, the 
scapulas vary less among themselves than do the arm-bones. 
There is, therefore, an antecedent probability that the shoulder- 
blade of any extinct member of the family would present fewer 
salient points of differentiation than the humerus. This con- 
sideration leads the writer to believe that a portion of a 
scapula which he had long ascribed to Hydrosaurus might well 
belong to the same pleurodont as the arm-bone which has been 
under notice; but, had this comparative sameness not been 
observed, it must be confessed that the differences from 
