274 VERTEBRATE ANIMALS, 
ORDER VI. SAUROPTERYGIA.—The Reptiles belonging to 
this order agree with the last in being all extinct, and in being 
confined to the Secondary period of geology. The best known 
are the Plestosaurz, which resembled the /chthyosauri in having 
all the limbs converted into swimming-paddles, but differed in 
several respects, of which the most obvious is the great elon- 
gation of the neck (fig. 149), The Plestosauri were gigantic 
marine Reptiles, chiefly characteristic of the formations known 
as the Lias and Oolites. As regards the habits of the Pleszo= 
saurus, Dr Conybeare concludes: “That it was aquatic is 
evident from the form of its paddles; that it was marine is 
almost equally so from the remains with which it is universally 
associated ; that it may have occasionally visited the shore, the 
resemblance of its extremities to those of the Turtle may lead 
us to conjecture ; its movements, however, must have been very 
awkward on land; and its long neck must have impeded its 
Fig. 149.—Plesiosaurus dolichodetrus. 
progress through the water, presenting a striking contrast to 
the organisation which so admirably fits the Ichthyosaurus to 
cut through the waves.” As its breathing-organs are such that 
it must of necessity have required to obtain air frequently, it 
may be inferred “that it swam upon or near the surface, arch- 
ing back its long neck like a swan, and occasionally darting it 
down at the fish which happened to float within its reach. It 
may perhaps have lurked in shoal-water along the coast, con- 
cealed amongst the sea-weed, and, raising its nostrils to a level 
with the surface from a considerable depth, may have found a 
secure retreat from the assaults of powerful enemies ; whilst the 
length and flexibility of its neck may have compensated for the 
want of strength in its jaws and its incapacity for swift motion 
through the water.” 
ORDER VII. PTEROSAURIA.—The Reptiles of this order are 
all extinct, and, like those of the preceding orders, are exclusively 
