X MAEINE EEPT1LES OF THE OXEOED CLAT 



Mycterosuchus, are much less specialised in this direction than the Geosauridse, 

 especially in the following points: — (1) the premaxillary region of the snout is 

 expanded, not pointed as in Metriorhynckus, and the prefrontals do not overhang the 

 orbits; (2) the neck is relatively rather longer; (3) the fore limbs, though reduced 

 in size, are not paddle-like ; (4) the end of the tail is not deflected to form the 

 support of a large terminal caudal fin, although there probably was a narrow dorsal 

 fin, at least on the terminal portion of the tail ; (5) the dorsal and ventral armour is 

 retained. Of the Teleosaurid*, Mycterosuchus is somewhat less specialised than 

 Steneosaurus, the fore limb being considerably larger in proportion to the hind limb. 

 Probably these reptiles were capable of dragging themselves out of the water on to 

 mud-banks, but it seems impossible that they can ever have moved any distance from 

 the water, as sometimes happens in the case of the modern Crocodiles. 



The Geosauridse, represented in the Oxford Clay by various species of Metrio- 

 rhynchus, have undergone extreme modification for a purely aquatic life. Thus the 

 head has a pointed snout, the prefrontals form a protective projection above the orbits, 

 the neck is shortened, the fore limb is paddle-like and very small compared with 

 the large hind limb, the terminal section of the tail is deflected and carried a large 

 vertical fin which, no doubt, was the chief means of propulsion. The dermal 

 armour has disappeared, but there is a well-developed sclerotic ring on the eye. 

 Some of the more slender forms (e. g., M. Iceve) show a complete loss of the cranial 

 sculpture, probably an advantage to an animal rapidly moving through the water. 

 E. Fraas *, Abel f , Arthaber £, and Auer § have described and discussed at great 

 length the various modifications undergone by the skeleton in this family, which 

 Fraas separated from the rest of the Crocodilia as a distinct group, the Thalatto- 

 suchia. He, for the most part, drew his descriptions and conclusions from Geosaurus, 



* "Die Meer-Crocodilier (Tbalattosuchia) des Oberen Jura," Palwontograpliica, vol. xlix. (1902) p. 1 : 

 " Eeptilien und Siiugethiere in ihren Anpassungserscheinungen an das marine Leben," Wiirttemberg. 

 Natunviss. Jalireshefte, vol. lxi. (1905) p. 347. 



t "Der Anpassungstypus von Mel^iol•hync7l,us, , ' Centralbl. f. Min. etc. 1907, p. 225. See also this 

 author's volume ' Palasobiologie ' (1912), p. 105 et seq. 



$ " Beitrage zur Kenntnis der Organisation und der Aupassungserscbeinungen des Genus Metno- 

 rhynchus," Beitrage Paliiont. Oester.-TJngarns, vol. xix. (190G) p. 2S7 ; also " TJeber den Anpassungstypus 

 von MetriorJiynchus," Centralbl. f. Min. 1907, p. 3S5. 



§ "Die Extremitaten von MelriorliyncJius," Centralbl. f. Mill. 1907, p. 53G ; " Weitere Beitrage zur 

 Kenntnis des Genus MetriorhywTius" torn, cit, p. 353. 



