244 HISTORICAL PALAZAONTOLOGY. 
swimming-paddles, whilst the skin seems to have been equally 
destitute of any scaly or bony investiture. Unlike the Jchthy- 
Fig. 177.—Plestosaurus dolichodeirus, restored. Lias. 
osaur, however, the Plestosaur had the paddles placed far back, 
the tail being extremely short, and the neck greatly lengthened 
out, and composed of from twenty to forty vertebrae. The 
bodies of the vertebree, also, are not deeply biconcave, but are 
flat, or only slightly cupped. ‘The head is of relatively small 
size, with smaller orbits than those of the /chthyosaur, and with 
a snout less elongated. ‘The jaws, however, were armed with 
numerous conical teeth, inserted in distinct sockets. As re- 
gards the habits of the Plestosaur, Dr Conybeare arrives at the 
following conclusions: ‘“ 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 resem- 
blance of its extremities to those of the Turtles may lead us to 
conjecture: its movements, however, must have been very 
awkward on land; and its long neck must have impeded its 
progress through the water, presenting a strong contrast to the 
organisation which so admirably fits the /cAthyosaurus to cut 
through the waves.” As its respiratory organs were such that 
it must of necessity have required to obtain air frequently, we 
may conclude ‘that it swam upon or near the surface, arching 
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 
