164 BRITISH FOSSIL REPTILES. 



brachium <ind the cnemion in tlio liiglier Vertebrates, being scarcely more marked or 

 differentiated in the present genus of huge Sauropterygia than in Icltthyopterygia. 



The first indication of the modification in question was given by a specimen 

 in which only the proximal halves of the two bones, or two chief bones, succeeding 

 the femur were preserved along with that bone. 



The inference which I drew from close inspection and comparison of the 

 preserved portions of the two cneraial bones was subsequently confirmed or 

 strengthened by the condition of the same segment of the fin-bones in the 

 instructive specimen of those bones restored by Mr. Mansel-Pleydell, j^i'obably 

 from the bones of the skeleton of the Pliosaurus grandis to which the above 

 described skull belonged, and of which fin-bones a cast is exhibited in the Palseon- 

 tological Gallery of the British Museum of Natural History. 



Nevertheless, with the close general affinities illustrated by most of the frame- 

 work and dentition of Plio- to Plesio-saunis, I waited in hopes of an opportunity 

 of acquiring certainty as to the structure of the middle segments of the limb before 

 committing myself to a publication of what I am now able to positively state to be 

 a generic character of Pliosaurus. 



The wished-for evidence reached me in the form of a block of Portland stone, 

 in which were embedded the femur, cnemion, tarsus, and part of the metatarsus 

 and digits of a right hind-limb, referable, l^y the character about to be described, 

 to the genus Pliosaurus. The specimen, moreover, had the additional interest of 

 being the first evidence of that genus from the Upper Oolite of Portland Island. It 

 is figured i-ather less than one-fourth the natural size in Sauropterygia, PI. 19, fig. 8. 



The femur (ib., C5) presents the usual plesiosauroid proportions and characters, 

 the pliosaurian affinity being faintly indicated, as usual, by the greater extent of 

 the tract external to the fibular division (above 67) of the distal articular extremity. 

 The tuberosity and contiguous rough surfaces for the attachment of muscles, at 

 and near to the proximal end, are also a little more strongly marked, as in the 

 Pliosaurus grandis, but the tuberosity is less distinctly prominent than in Pliosaurus 

 trochanterius. The head of the femur, subconvex and oblong, is slightly nipped 

 in, as it were, near its outer third part from side to side ; the long axis of this 

 surface is at right angles to the plane of the expanded and compressed distal 

 end of the bone. A few of the crateriform elevations on the rough articular 

 surface are preserved. The inner side of the bone is exposed in the block of 

 matrix. The roughness for ligamentous or tendinal attachment ceases about one 

 third of the way down the shaft. This part, gradually contracting, assumes first a 

 circular transverse section, then becomes compressed from without inwards instead 

 of from side to side, increasing in breadth and diminishing in thickness to the 

 distal articular end. The surfaces for tibia (GO) and fibula (G7) are indicated by, or 

 meet at, a widely open angle. The projecting part of the femm- beyond the tibial 

 surface is rounded off ; that beyond the fibula is, as above remarked, of gi'eater 



