wae GREAT SEA-LIZARDS 81 
were the chief swimming organs. The vertebre of this short tail 
show that it probably was highly flexible, and could move rapidly 
from side to side; but, for all that, its use as a propeller would 
not be of much importance. We see now why the paddles are 
so long and powerful, like two pairs of great oars, one pair on 
each side of the body. In a fossil skeleton you will notice the 
flattened shape of the arm-bone (or humerus), and of the thigh- 
bone (or femur). This gave breadth to the paddles, and made 
them more efficient as swimming organs. They give no indica- 
tion of having carried even such imperfect claws as those of 
turtles and seals, and therefore we may conclude that the Plesio- 
saur was far more at home in the water than on land, and it 
seems probable that progression on land was impossible. 
The tail was probably useful as a rudder, to steer the animal 
when swimming on the surface, and to elevate or depress it in 
ascending and descending through the water. Like the fish- 
lizard, this creature was an air-breather, and therefore was obliged 
occasionally to visit the surface for fresh supplies of air. But 
probably it possessed the power of compressing air within its 
lungs, so that the frequency of its visits to the surface would 
not be very great. 
From the long neck and head, situated so far away from the 
paddles, as well as for other reasons, it may be concluded that 
this creature was a rapid swimmer, as was the Ichthyosaurus. 
Although of considerable size, it probably had to seek its food, 
as well as its safety, chiefly by artifice and concealment. The 
fish-lizard, its contemporary, must have been a formidable rival 
and a dangerous enemy, whom to attack would be unadvisable. 
Speaking of the habits of the long-necked sea-lizard, Mr. Cony- 
beare, in his second paper, already alluded to, says, “That it was 
aquatic, is evident from the form of its paddles; that it was 
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