Plesiosanrus, a genus of the extinct reptilian group, the Plesiosauria, including numerous species, some of which reach a length of twenty feet. It occurs from the Lower Lias to the Chalk; but allied forms are found in the Trias. The head is comparatively small, with one occipital condyle; nostrils far back; slender, curved, sharp, striated teeth, in distinct sockets, unlike Ichthyosaurus (q.v.); and without sclerotic plates round the eye. The neck is long and slender, and the tail proportionately short; but there are in all sometimes more than 90 vertebra?. The fore and hind limbs are very similar, longer than in Ichthyosaurus, but modified as swimming flippers. There are only five rows of digital phalanges. Though very perfect skeletons have been found in the Lias, there is no evidence of scales or scutes. The genus is represented in Britain, on the Continent, in India, Australia, and North and South America.