256 PALEONTOLOGY. 



FAM. DlCYNODONTIA. 



A long ever-growing tusk in each maxillary bone ; pre-maxil- 

 laries connate, forming with the lower jaw a beak- 

 shaped mouth, probably sheathed with horn. 



The evidences of this most singular family of reptiles have 

 hitherto been found only in South Africa, where they occur, 

 petrified, in a hard stone of probably triassic age. In the 

 modifications of the skull may be discerned characters of 

 the crocodile, tortoise, and lizard, coupled with the presence 

 of a pair of huge sharp-pointed tusks, growing downwards, 

 one from each side of the upper jaw, like the tusks of the 

 mammalian morse (Trichecus). No other kind of teeth were 

 developed in these singular animals ; the lower jaw appears 

 to have been armed, as in the tortoise, by a trenchant sheath 

 of horn. 



The vertebras, by the hollowness of the co-adapted articular 

 surfaces, indicate these reptiles to have been good swimmers, 

 and probably to have habitually existed in water ; but the 

 construction of the bony passages of the nostrils proves that 

 they must have come to the surface to breathe air. The pelvis 

 consists of a sacrum composed of 5 confluent vertebrae, with 

 very broad iliac bones, and thick and strong ischial and pubic 

 bones. The bones of the limbs resemble those of the marine 

 chelonia, but are more expanded at the extremities. 



Some extinct plants allied to the Lepidodendron, with 

 other fossils, render it probable that the sandstones containing 

 the dicynodont reptiles were of the same geological age as 

 those that have revealed the remains of the Ehynchosaurs and 

 Labyrinthodonts in Europe. 



The genus Dicynodon, from the Greek words signifying 

 " two tusks or canine teeth,"* was founded on four species 



* Trans. Geol. Soc, 2d series, vol. vii. (dis, two ; Jcunodos, canine-tooth). 



