THE PLESIOSAURS 2459 



severe, and the natives are not tmfrequently bitten by them in India and Burma 

 while 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, how- 

 ever, 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 carcasses 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 until 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 long 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 f 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 SAUROPTERTGIA 



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 

 downward 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 

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

 the ribs, as well as in the want of a breastbone or sternum. In the skull the 

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



