216 PALEONTOLOGY 



the vertebrae in the same column, that although specimens 

 from the tail, and from different parts of the back, have been 

 obtained, no cervical vertebra with any probability belonging 

 to this genus has yet been found. The caudal centrum presents 

 two well-defined, rather prominent, hypapophyses for the 

 haemal arch. 



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 palaeonto- 

 logical catalogues an Ichthyosaurus Lunevillcnsis (De la Beche), 

 a Plesiosaurus Lunevillcnsis (Minister), and a Chelonia Luncvil- 

 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 " 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 whole class Reptilia ; the lower jaw presents 

 a like excessive development of the coronoid processes. 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 Invertebrata. 



The teeth of the upper jaw consist of an external or 

 maxillary series, and an internal or palatal series. The 



