REPTILIA. 



53 



No. 79. [237] Placodus gigas, Agassiz. 



Skull (cast). This reptile (formerly 

 called a fish) was a Plesiosaurian, ac- 

 cording to Owen, breathing the air like 

 Cetaceans. No part, save the head has 

 been found. The cranium *is as broad 

 as long, the figure viewed from above 

 being that of a right-angled triangle 

 with the corners rounded off. No other 

 number of the class has such wide tem- 

 poral fossae and strong zygomatic arches ; 

 the lower jaw, moreover, presents an 

 excessive development of the coronoid 

 process. These developments, for great 

 size and power of action of the biting 

 and grinding muscles, relate to a most 

 extraordinary form and size of the teeth, 

 which resemble paving stones, and were 

 evidently adapted to crack and bruise 

 shells and crusts of marine Inverte- 

 brates. The palatal teeth, three on 

 each side, are of large size; the maxillary teeth, four in number, are much 

 smaller; thepremaxillary teeth, three in each ramus, are elongated and conical. 

 The palatal are relatively larger than the teeth of any known animal, living 

 or fossil. All these teeth are implanted in distinct sockets. This skull was 

 found in the Muschelkalk (Trias) at Laineck, Bavaria, and belongs to the 

 University Museum of Munich. Size, 7x5. 



ORDER MOSASAURIA (Pythonomorpha). 



This order includes tlie huge elongated creatures typified by 

 the Mosasau7'us^ and formerly classed with the Lacertilia. They 

 were eel-like in form and movements, and probably the most 

 elongated of reptiles, some attaining a length of perhaps eighty 

 feet. The feet were modified to form slender paddles. Small 

 scales probably covered the body. The head was pointed, flat, 

 with eyes nearly vertical. Four rows of rootless teeth were 

 borne in the upper jaw, and each half of the lower jaw had a 

 unique articulation near the middle whereby the creature was 

 enabled to swallow large prey, for while, like serpents, the rami 

 were loosely joined in front by ligaments there was not as free 

 movement of the quadrate bone. Their affinities are with 

 Lizards and Snakes, and slightly with Satn'oiyterygia. Cope 

 makes six genera of the order. 



The Mosasauria seem to have been the most abundant and 



