60 



GEOLOGY. 



series of remains of reptilia from the Trias of S. Africa referred by 

 Prof. Owen to the genera Lycosaurus^ Ptychognathus, Oudenodon, 

 JEndothiodon, &c. 



Chelonia. — In Wall-cases 6 and 7, and in Table-cases 17, 18, 19, 

 and 20, are placed the fossil remains of the order Chelonia, in which 

 are included Tortoises and Turtles, a group of reptiles in which the 

 backbone and ribs are immovable, being combined with the external 

 coat of bony plates, closely soldered together, enclosing the entire body 

 of the animal. This box-like envelope is covered with leathery skin or 

 horny plates ; one kind of which is called " tortoise shell," and is made 

 into combs, &c. The bones of the skull (except the lower jaw and 

 the hyoid bones) are also consolidated. They have no teeth, but the 

 jaws being encased in a horny beak, the sharp edge serves instead 

 for dividing the food. 



The Chelonians are found living at the present day on land, in 

 fresh water, and in the sea; they are all oviparous, depositing their 

 eggs in the sand, to be hatched by the warmth of the sun. Some 

 recent Turtle's eggs from Ascension, cemented together and 

 fossilized in shell-sand by deposition of lime, produced by evapora- 

 tion of sea-water, are placed in Table-case No. 18. 



Some of the old gigantic land-tortoises (of which a few only survive) 

 inhabited Mauritius and other islands of the Indian Ocean and the 

 Galapagos Islands in the Pacific. Like the Dodo, they have been 

 gradually exterminated by the hand of man. The largest of the fossil 

 forms (a restored cast of which is placed on a stand at the west-end 

 of this gallery) is the Colossochelys atlas from the Sewalik Hills of 

 India. The detached fragments {vouchers for the size of this great 

 carapace) are placed in the adjacent Wall-case (7). These old land- 

 tortoises, so remarkable for the magnitude they attained, had ex- 

 tremely long necks and small heads; they were all vegetable-feeders 

 and quite harmless. 



Several smaller species of Chelonians are also to be seen in this case 

 from the same Indian locality. 



In Wall-Case 6 are placed the remains of the great Chelone 

 Hoffmanni from the Chalk of Maestricht; the Chelone gigas, 

 Owen, whose head and some other parts are exhibited here, from 

 the London clay of Sheppey, was even larger. These were true 

 marine turtles, related to the " Loggerhead " Turtle of the present 

 day. 



One small species of Umys, or Marsh Tortoise, was formerly an 

 inhabitant of this country, and its remains have been found fossil in 

 Norfolk. 



The oldest Chelonians we know are found fossil in the Great 

 Oolite formation, but judging, from certain footprints in the Triassic 

 sandstones, they may have existed at even an earlier date. 



In Wall-case"lO, and in Table-case No. 16, are placed the remains 

 of one of our largest marine reptiles, the Pliosaurus^ found fossil in 

 the Kimmeridge clay near Ely, and also in Dorsetshire. We have 

 no entire skeleton of this animal, but a single swimming-paddle 



