KIIOKOSA VliXJS Q L ' KEN SLA NDICUS. 
The buttress-like process in these bones of Kronosaurus, whether inter- 
preted as a trochanter or as a tuberosity, appears to have been more prominent 
than the corresponding structures in Megalneusaurus, Pliosaurus, or Peloneustes. 
A pronounced depression on the postero-external surface of the longer 
specimen, below the buttress-like process, probably marks the insertion of 
powerful coraco-brachiales muscles, which pulled the humerus backwards and 
downwards. 
The abraded surfaces are somewhat coarsely cancellous in appearance, and 
when viewed under a lens a curious irregular honeycombed effect is noticeable. 
There are two fragments, over 200 mm. in length, in this series, which 
come from the distal end. These have been cleft in the median line of the 
main axis. Probably they represent the distal end of the same long bone, but 
since the initial cleavage so much abrasion has taken place that this cannot be 
positively stated. When placed in juxtaposition these two fragments present a 
distal end of about 400 mm. in antero-posterior width, with a maximum 
thickness of 134 mm. in the central region. In cross-section the bone is a 
flattened oval, and towards the anterior and posterior borders the thickness is 
much reduced. The articular area is fairly complete, but the fractures on the 
shaft are very irregular. 
Embedded in a mass of matrix on the articular surface are the proximal 
remains of two bones, the radius and ulna, assuming the fragments to represent 
a humerus. Prolonged abrasion has so reduced these antebrachial elements that 
no useful information can be gained from them, but the ventral surface of the 
radius may have been very concave. 
D. M. S. Watson in his interesting studies of the Elasmosaurid Shoulder- 
girdle and Forelimb. 8 and his reconstruction of the musculature from relatively 
well-preserved bones, points out that the Plesiosaur limb “ is essentially a rigid 
oar.” In the large-headed types with elongated humeri, the structure of the 
fore-limb and girdle provided the mechanism for swift movement in ocean 
waters. Watson suggests that these large-headed forms, with their enormous 
gape, fed on large animals which were captured by superior speed. 
C. W. Andrews’s restoration, of the skeleton of Peloneustes philarchus, 
from his valuable Catalogue of the Marine Reptiles of the Oxford Clay, 
published by the British Museum, has been reproduced (Text-figure 5) to illustrate 
the general structure of a Pliosaur. 9 
Acknowledgments. 
I am indebted to Dr. Anderson, of the Australian Museum, Sydney, for 
a transcript of W. C. Knight’s paper on Megalneusaurus from the American 
Journal of Science, and to Mrs. Estelle Thomson for her excellent drawings. 
1924 : D. M. S. Watson, P.Z.S., p. 914. 
1913: C. W. Andrews, Catal. Mar. Kept. Oxford Clay, pt,. 2, Brit. Mus. 
