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EXPLANATION OP PLATE 19 . 
Plate 19. V. I. p. 205. 
Fi 1, yV bcEiutiful spEcinicii of Plcsiossiuvus uiacrocc- 
phalus hitherto uudescribed, found in the Lias marl 
at Lyme Regis by Miss Aiming, and now in the 
collection of Lord Cole. (Original.) 
On comparing this figure with those of P. Dolichodeirus 
at PI. 16, 17. The following difierences are obvious : 
1. The head is very much larger and longer, being 
nearly one half the length of the neck. 
2. The vertebrsB of the neck are thicker and stronger in 
proportion to the greater weight they had to sustain. 
3. The hatchet-shaped bones differ in form and size, as 
may be seen by comparing them with those of P, dolicho- 
deirus. PI. 19. Fig. 2. and PI. 17. 
4. The bones of the arm and thigh are shorter and 
stronger than in P. Dolichodeirus, and corresponding dif- 
ferences may be traced throughout the smaller bones of the 
Paddles; the general adjustment of all the proportions 
being calculated to produce greater strength in the P. Ma- 
crocephalus, than in the more slender limbs of P. Dolicho- 
deirus. 
These differences are not the effect of age ; as the two 
specimens, from which they are here described, are nearly 
of the same length. 
Fig. 2. Hatchet-shaped bones of the neck of Plesiosaurus 
Dolichodeirus, copied from the specimen figured in 
PI. 17. 
3, Anterior extremity of an insulated lower Jaw of Ple- 
siosaurus, from the Lias at Lyme Regis, in the Bri- 
tish Museum, part of the collection of Mr. Hawkins. 
V. I. p. 205. Note. (Original.) 
4. The entire bone, of which Fig. 3. forms part, reduced 
to a small scale. 
