CROCODILIA. 223 



numerous conical prehensile teeth, a very long mobile trunk, and 

 fin-like extremities as in the Whales. 



Fam. No thesauri! (Sauropterygii Owen). With elongated bones of the 

 upper jaw which reach to the point of the long snout ; without superior temporal 

 bones ; with simple conical teeth. Belong to the Trias. Nothosaurus mirabil'is 

 Miinst. ; Simosaurus H. v. M., and others. 



Fam. Plesiosaurii {Sauropterygii Owen). With long snake-like neck, short 

 head and tail, and elongated swimming fins. They lived in the Jura and the 

 chalk. Plesiosaitrus Conyb. 



Fam. Ichthyosauri! (JLcldliyopterygii Owen). With very short neck, thick 

 elongated body, short swimming fins, and long tail probably surrounded by a fin. 

 The snout, pointed and elongated like a beak, is principally formed by the 

 prasmaxillary bones. The teeth present a striated and folded surface, and are 

 closely crowded together. They are found principally in the Jura, rarely in 

 the chalk. Ichthyosaurus communis De la Beche, etc. 



Order 2. CROCODILIA (LORICATA). 



Hydrosauria, with bony dermal plates and teeth wedged into the 

 bones of the jaws, to which they are confined; with four partly clawed 

 feet and long, keeled sivimming tail. 



The extremities no longer have the form of swimming fins, but of 

 freely articulated legs and feet with separated digits. The integu- 

 ment is granular and leathery, and contains, especially on the dorsal 

 surface, large and in part keeled, osseous plates. On the tail these 

 plates form a dentated crest, paired in front, but in its hinder part 

 simple. 



The broad flat skull is distinguished by the corroded appear- 

 ance of the surface of the bones, and possesses separated alisphenoids, 

 and above the maxillo-jugal arcade a supra- temporal arcade, which 

 is separated from the orbit by a bony bridge (process of the post- 

 frontal and jugal). The roof of the skull is formed by an unpaired 

 parietal and frontal, to which are joined the paired nasal bones. The 

 upper jaws are firmly united with the skull and are elongated so as 

 to form a long snout, at the end of which the paired prsemaxillary 

 bones are wedged in. The sides of the snout are formed by the 

 maxillary bones which are very large. The praemaxillaries, which 

 bound the nasal apertures, and the maxillaries develop horizontal 

 palatal plates, which meet in the middle line and form the anterior 

 part of the hard palate. The iacrymal is always of considerable 

 size. Behind, the palatine and pterygoid develop palatal plates which 

 unite suturally in the median line, and constitute a completely closed 



