xin. PLEIOSAURUS MACROMERUS. 357 



(1841, p. 63), as belonging to pleiosaurus. Another of the same 

 kind was obtained from the Kimmeridge clay of Swindon. They 

 appear to belong to the large animal already mentioned, Plesio- 

 saurus macromerus. The articulating faces are swollen and pro- 

 minent in the middle, and this umbo is encircled by a broad shallow 

 depression within the raised and somewhat revolute border. The 

 transverse processes were borne on projecting bases, from which 

 they have been separated without fracture. The bases of the 

 hsemapophyses were widely separated and placed at the ends of 

 longitudinal ridges. The sides of the vertebra are much com- 

 pressed. 



Length, 3-0 inches ; breadth, 4-8 ; height to the canal, 4% in 

 the specimen from St. Giles's : or, if length be taken as 100, breadth 

 = 1 60, height = 140. 



Length, 3-0 inches; breadth, 5*2 ; height, 4*4, in the specimen 

 from Shotover : or, if length be taken as 100, breadth = 173, height 



= 147- 



Dimensions of large femur, length, 34-0 inches ; breadth near 

 distal end, 12*75; over proximal end (which is compressed), 8*4; 

 in the middle of the shank, 7*25 ; thickness at the distal end, in the 

 middle, 2'5. (See Diagram CLIX. p. 362.) 



Comparing these proportions with those given for Pleiosaurus 

 brachydeirus, the difference is very considerable. The general form 

 is also different, the sides being more nearly on equal slopes and 

 curves, especially in the smaller one ; the bone much more com- 

 pressed generally; and the distal edge fitted to thinner tibial and 

 fibular associates. The head of the bone is in some degree ridged 

 in the middle; and the interior surface for a space of 6 inches 

 below the head is roughly ridged and furrowed, somewhat after the 

 pattern of Pleiosaurus grandis, Owen, from which, however, it 

 differs in form, relative breadth, and thickness. When placed by 

 the huge femur (or humerus) from Kimmeridge, which is of fully 

 equal size, a difference of form, though less marked, is quite 

 manifest in the distal end, which in that species is not cut to 

 a similar sweep, but has the usual doubly-cut edge for adaptation 

 to the tibia and fibula. These species must, however, be nearly akin. 



Of the femur (or humerus) there are three well-marked specimens, 

 two probably making a pair of larger size ; one smaller. 



Small femur, 23-0 inches long; 8-5 wide at distal end; 4-2 at 



