RHYNCHOCEPHALIA. 183 



into the lower lobe of which the hindermost caudal vertebra) extend. 

 A similar caudal fin has been found in the Lithographic Stone (U. Juras- 

 sic) of Bavaria. It is also noteworthy that the hinder end of the vertebral 

 column is sharply bent downwards in several .skeletons from the English 

 Lias. The largest known species occur in the Lias, the skull of /. tri- 

 gonodon, from the Upper Lias of Banz, Bavaria, attaining a length of 

 about two metres, while the total length of this animal cannot have 

 been less than ten metres. 1. platyodon, from the Lower Lias of Lyme 

 Regis, Dorsetshire, must have been nearly as large. /. intermedium and 

 7. communis, of moderate size, are the commonest species in the English 

 Lower Lias. Various fragments, more or less unsatisfactory, seem to 

 indicate that Ichthyosaurus ranges from the Rhtetic to the Lower 

 Chalk inclusive ; while those of Cretaceous age occur not only in Europe 

 but also in the East Indies, Australia, New Zealand, and South America. 

 Two vertebral centra are also recorded from the neighbourhood of Mom- 

 basa, East Africa. 



Ophthalmosaurus (fig. 1 13 B). This is an Upper Jurassic and Lower 

 Cretaceous genus in which the teeth are either absent in the adult or are 

 minute and confined to the front of the jaw. The pubis and ischium are 

 fused together, leaving a small obturator foramen. The humerus and 

 femur exhibit three distal facettes for the bones of the second segment 

 of the limb, these being apparently the ordinary two elements with the 

 addition of a sesamoid bone on the ulnar (fibular) side (fig. 113). All 

 the elements of the carpus, tarsus, metacarpus, metatarsus, and phalanges 

 are more or less rounded or oval in shape, the ossifications not fitting 

 together, but having been originally surrounded each by a layer of per- 

 sistent cartilage. The typical species is 0. icenicus from the Oxford Clay 

 of Peterborough, and there is doubtful evidence of the genus on so high 

 an horizon as the English Upper Greensand. Baptanodon, from the 

 Jurassic of Wyoming, U. S. A., is remarkably similar to the European 

 fossil, and perhaps generically identical. 



ORDER 5. RHYNCHOCEPHALIA. 



The snicall lizard-like Sphenodon or Hatteria now existing in 

 certain islands off New Zealand, is the sole survivor of an order 

 which is already clearly recognizable in the Permian, and seems 

 to have attained its maximum specialization so long ago as the 

 Triassic period. The order is named RHYNCHOCEPHALIA in 

 allusion to the beak-shaped rostrum of several of the typical 

 genera. So far as can be determined, its earliest members, like 

 the latest, are characterized (i.) by a well-defined upper and 

 lower temporal arcade, (ii.) by a large fixed quadrate buttressed 



