236 PALEONTOLOGY. 



The coracoid in the contraction of the body reminded Cuvier 

 of that of the Ichthyosaurus, but its expanded median part was 

 differently shaped. The pubis, like that of the Plesiosaurus, 

 resembles to a certain degree the pubis in Chelonia. The few 

 bones of the limbs which have been found still more resemble, 

 as do those of Pistosaurus, the corresponding bones of marine 

 Chelonia. Accordingly, there have been entered in paheonto- 

 logical catalogues an Ichthyosaurus Lunevillensis (De la Beche), 

 a Plesiosaurus Lunevillensis (Mlinster), and a Chelonia Lunevil- 

 lensis (Gray and Keferstein) ; but all these are parts of one and 

 the same genus of Enaliosaurian, — the " Saurien des environs 

 de Luneville " of Cuvier, the 6i Simosaurus " of H. von Meyer. 



Genus Placodus. — The cranial structure in this genus of 

 muschelkalk reptile is closely similar to that in Simosaurus, 

 but its proportions are different ; it is as broad as long ; the 

 greatest breadth being behind, whence the sides converge to 

 an obtuse muzzle ; the entire figure viewed from above being 

 that of a right-angled triangle, with the corners rounded off. 

 The temporal fossae are the widest, and zygomatic arches the 

 strongest, in the Eeptilian class ; the lower jaw presents a 

 concomitant development of the coronoid process (fig. 96, c, 

 29). These developments, for great size and power of action 

 of the biting and grinding muscles, relate to a most extra- 

 ordinary form and size of the teeth, which resemble paving- 

 stones, and were evidently adapted to crack and bruise shells 

 3,nd crusts of marine Invertebrata. 



The teeth of the upper jaw consists of an external or 

 maxillary series, and an internal or palatal series. The 

 maxillary series are supported in a marginal row of alveoli by 

 the premaxillary (ib. 22) and maxillary (ib. 21) bones ; the 

 palatal series are implanted in the palatine and pterygoid 

 bones. The maxillo-premaxillary teeth are five in number on 

 each side, two (ib. a, b,) implanted in the premaxillary, and 

 three (ib. c, d, e) in the maxillary. The premaxillary teeth 



