622 KEPT I LI A. 



Hatteria to the Triassic Rhynchocephalia ; but we have no 

 example of a Reptilian genus which has persisted from age 

 to age as Ceratodus has done among Fishes. It follows 

 naturally from this linking of the present with the past, that 

 among the fossil forms we find "generalised" types, types 

 which exhibit affinities with groups which in our classifica- 

 tion of recent forms may be very widely separated. It is 

 indeed, as has been said, only because of our ignorance of 

 their past history that we are able to classify living genera 

 into separate orders at all. 



The following types of extinct reptiles seem to have 

 entirely disappeared :- 



Theromorpha or Anoinodontia. Lizard-like terrestrial animals with 

 limbs adapted for walking, found in the Permian and Trias. The 

 group shows a remarkable combination of reptilian and mammalian 

 characters. In illustration of reptilian characters we may note the 

 pineal foramen, the complex lower jaw, the usual presence of pre- and 

 post- frontals. Mammalian features are illustrated in some types by 

 the differentiation of the teeth into incisors, canines, and molars ; by a 

 single temporal arcade like a zygomatic arch ; by the way the limbs 

 raise the body off the ground ; by the union of the pelvic bones into 

 an os innominatum ; by the reduction of the quadrate ; by the share the 

 squamosal may take in forming the articulation for the lower jaw. 

 Examples. Pareiosaiirus, Galesaurus, Dicynodon. 



Plesiosauria. Amphibious and marine reptiles represented from the 

 Trias to the Chalk, without exoskeleton, usually with a long neck and 

 short tail. The skull has a single broad temporal arcade, pterygoids 

 meeting in the middle line, fixed quadrates, and a pineal foramen. 

 There are strongly developed pectoral and pelvic girdles. The limbs 

 vary ; in the earlier, more generalised, forms they are adapted for 

 walking on land ; but in the more specialised types they are modified 

 into powerful paddles, like those of Chelonia. The nearest affinities 

 are with the Chelonia. Nothosaurus had limbs adapted for progression 

 on land ; Plesiosaunis (40 ft. in length) and Pliosannis were carni- 

 vorous forms adapted to an aquatic life. 



Ichthyosanria. - - Large marine carnivorous Reptiles, represented 

 from the Trias to the Chalk, with tapering body like that of a shark, 

 large dorsal and caudal fins, and two pairs of paddle-like limbs. In 

 the paddle the number of digits may be more than five, and the 

 phalanges of each digit are often very numerous. The pectoral arch 

 consists of coracoids, scapulae, clavicles, and a T-shaped interclavicle, 

 but there is no sternum. The skull has a long tapering rostrum, large 

 orbits, a large parietal foramen, and usually sharp conical teeth in a 

 continuous groove. The vertebrae are deeply amphicoelous. There was 

 no dermal armour. The length of the body is sometimes 30 to 40 ft. 

 Some species were viviparous. 



Examples. Ichfhyosannis, Ophthalmosawiis. 



