398 AXOMODONTIA. 



and France. Mesosaurus(p, 334) is supposed by some authors to belong here. 

 Fam. 2. Plesiosauridae. The limbs are paddle-shaped and adapted 

 for swimming ; the radius and ulna and tibia and fibula are shortened, 

 and the number of phalanges, which are elongated, is increased. An inter- 

 pterygoid vacuity is present in the palate. An epipterygoid is present. 

 The neck is long with 30 to 40 cervical vertebrae. The cervical ribs are 

 single- or double-headed. The coracoid symphysis is much extended 

 antero-posteriorly and the scapulae tend to meet in a median ventral 

 symphysis. Plesiosaurus Conybeare, Lias of England and Germany. 

 Eretmosaurus Seeley, L. Lias, England. Rhomaleosaurus, Colymbosaurus, 

 Muraenosaurus Seeley, U. Jurassic, England. Cryptoclidus Seeley, all 

 ribs single-headed, U. Jurassic, England. A number of diverse genera 

 from the U. Cretaceous of N. and S. America and N. Zealand. Plio- 

 saurus Owen, with relatively large head and short neck (20 vertebrae), 

 Lias to U. Jurassic. England, Europe, India. Megalneusaurus Knight, 

 largest known Plesiosaur, U. Jurassic, Wyoming, U.S. Elasmosaurus 

 Cope, U. Cretaceous, Kansas, U.S. Polyptychodon Owen, M. and U., 

 Cretaceous, England, Germany, Russia. 



Sub-class 8. ANOMODONTIA.* 



Terrestrial reptiles with limbs adapted for the support of the body, with 

 biconcave vertebrae, fixed often reduced quadrate, and pineal foramen. The 

 temporal fossa is completely closed by the bones of the temporal region or there 

 is a broad temporal arcade. The bones of the pectoral and pelvic girdles are 

 fused or immoveably connected by suture. Permian and Triassic formations 

 of Europe, N. America, S. Africa, and India. 



The Anomodontia form a somewhat diverse group of apparently terres- 

 trial reptiles. They are known by remains which are in most cases 

 imperfect, and it is highly probable that the sub-class will eventually have 

 to be broken up. The group however as it stands combines a number 

 of reptilian features not found together in any other reptilian sub-class 

 with some highly remarkable mammalian characteristics. Of their 

 essentially reptilian features, we may mention the pineal foramen, the 

 quadrate, the compound mandible, the general presence of pre- and post- 

 frontals. To show the peculiar combination of characters found in no 

 other reptilian group, we may draw attention to the union of the upper 

 and lower temporal arcades into one broad arcade, unpierced as a rule by 

 a lateral temporal fossa and found elsewhere only in Plesiosauria and 

 Ichthyosauria ; to the frequent presence of a secondary palate, which 

 recalls that of the Chelonia ; to the thecodont dentition which is found 

 also in Plesiosauria, but not in the two other groups ; to the structure of 

 the pelvis which is quite different from that of any of the three above- 

 mentioned groups ; and to the absence of abdominal ribs. 



The mammalian characters are however those which preeminently 

 distinguish them from other reptiles. These are : the frequent differentia- 

 tion of the teeth into incisors, canines and molars (Fig. 222) ; the resem- 

 blance of the single temporal arcade to the mammalian zygomatic arch ; 

 the mammalian character of the limbs which carry the body high above 

 the ground (Fig. 221) ; the union of the pelvic bones into an osinnomina- 

 tum (Fig. 221) ; and the continuity of the pubic and ischiadic symphysis ; 



* Sometimes called Theromorpha. 



