. Reptiles aquatiques du passé et du présent . sasaurs. L'extrémité du museau a une projection semblable à un bec. Les dents sont beaucoup plus longues, plus pointues et plus récurées que la plupart des reptiles terrestres, ce qui indique leur utilisation pour la capture et la rétention de proies glissantes et rapides. Les nervures à tête unique sont courtes, ce qui prouve que le corps wasslender et sans doute cylindrique, plus comme celui d'un serpent. Les 136 REPTILES AQUATIQUES DE LA queue PASSÉE ET PRÉSENTE étaient non seulement considérablement allongés, mais ils étaient aussi compressédés en un organe propulseur plat et efficace dans l'eau. Mise à plat du

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. Water reptiles of the past and present . sasaurs. Theextremity of the snout has a beak-like projection. The teeth aremuch longer, more pointed, and more recurved than is the casewith most land reptiles, indicating their use for the capture andretention of slippery, quick-moving prey. The single-headed ribs are short, proving that the body wasslender and doubtless cylindrical, more like that of a snake. The 136 WATER REPTILES OF THE PAST AND PRESENT tail was not only enormously elongated, but it was also compressedinto a flat and effective propelling organ in the water. Thisflattening of the tail is apparent from the skeleton, with its elongatedchevrons below and spines above, and it is also proved by the for-tunate preservation of the extremity of the tail of one specimen, showing not only the impressions of the scales in the matrix, butalso the outlines that the soft parts had in life. To quote fromLortet, in translation: The tail was covered wholly with smallscales, regularly hexagonal in shape, shining and nacreous, larger. Fig. 64.—Life restoration of Pleurosaurus on the under side than above. The upper border of the tail wassurmounted by a broad crest, extending to its extremity, and com-posed of large, oval scales. The body doubtless was whollycovered with scales, though it is not probable that the caudalcrest continued along the back. The limbs begin to show an aquatic adaptation, though notvery pronounced. They are much shorter and smaller than arethose of land-crawling reptiles; and the bones of the second series, that is, the radius and ulna, tibia and fibula, are relatively short, the beginning of adaptation to water habits. It is very probablethat the feet were webbed, though the fifth digit, as usual, is shorterthan the fourth. Doubtless on land the creature moved about PROTOROSA URIA 13 7 in a serpentine way, for it could not have progressed very rapidlyby the aid of its legs alone. The hind legs are longer than thefront legs, and they were connected

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