PLESIOSAURS. 101 



is very severe ; and the natives are not imfrequently bitten by them in India and 

 Burma whilst bathing. All the members of the typical genus, together with 

 Cantor's soft-tortoise and the chitra, are known to be carnivorous, and it is 

 commonly believed that the same is the case with the other members of the group. 

 According, however, to Dr. J. Anderson, this is incorrect with regard to the 

 granulated soft-tortoises of India, which he expressly states to be exclusively 

 vegetable and grain-feeders. The larger species probably feed both on fish and 

 other aquatic animals, and on the flesh of such carcases as may be floating in the 

 rivers they inhabit. In correlation with their asserted herbivorous habits, 

 the small granulated species do not snap and bite after the manner of their 

 larger cousins. On shore, according to the observer last mentioned, when left to 

 themselves, these species will slowly and cautiously extend their necks, and when 

 approached, instead of attempting to escape, withdraw rapidly into their shells, 

 of which the upper and lower anterior margins then meet. It is stated that all 

 the species are chiefly nocturnal, remaining during the daytime partially or 

 completely buried in the mud at the bottom of the water, and not beginning 

 to swim till sundown. Such species as inhabit marshes or swamps, liable to 

 be dried up during the hot season, bury themselves in the mud, at no great 

 depth below the surface, during the period of drought. As these tortoises 

 are known to remain frequently for a period of from two to ten hours, and 

 occasionally as much as fifteen hours, beneath the water, without coming to 

 the surface to breathe, it is obvious that they must have some special means of 

 oxygenating their blood. It is probable, indeed, that certain filamentous 

 appendages of the mucous membrane of the throat found in these tortoises 

 subserve the office of gills, and thus enable the blood to be renovated by means 

 of the atmospheric air dissolved in the water they inhabit. With regard to 

 their breeding-habits, it appears that the females of the granular shelled species 

 scrape a shallow hole in the mud, in which the eggs are laid and then carefully 

 covered up, the eggs themselves being round, and about an inch in diameter. 



The Plesiosaurs or Long-Necked Marine Lizards. 

 Order Sauropterygia. 



Strikingly different in appearance as are the skeletons of the members of the 

 two groups, it appears that, on the whole, the nearest allies of the tortoises and 

 turtles are those extinct reptiles known as plesiosaurs, or long-necked marine 

 lizards, whose range in time embraced the whole of the great Secondary period, 

 during which were deposited the vast series of strata extending from the Chalk 

 downwards through the Oolites to the Lias and Trias. These reptiles agree with 

 the tortoises in that all or nearly all of the ribs of the back are articulated to the 

 vertebras by single heads, and in the absence of hook-like (uncinate) processes to 

 the ribs, as well as in the want of a breast-bone or sternum. In the skull the 

 quadrate-bone is immovably fixed, and the palate more or less completely closed. 

 Both groups have the lower bones of the pelvis expanded into large flat plates, 

 and there is also a similarity in the structure of the bones of the limbs. 



Whereas, however, the tortoises have the upper surface of the body covered 



