CROCODILES. 327 



elevation of seven thousand feet, and Plectrurus Perrotetii is found 

 between five thousand and eight thousand feet. 



Fossil remains of serpents are not numerous, and only one spe- 

 cies, the Simoliophis Rochebruni, from the Upper Cretaceous de- 

 posits of the Charente, France, is known to antedate the Tertiary 

 period. Several species of Palseophis, considered by some authors 

 to have been closely related to the boas, which they rivalled in size, 

 and by others to constitute the type of a distinct family, have been 

 found in the Lower Eocene deposits (Londonian) of England, France, 

 and Italy ; two or three species have been likewise described from 

 the nearly equivalent deposits of the State of New Jersey.* Boae- 

 form serpents appear to be indicated by the Python Eubceicus, 

 from Kumi, in the island of Euboea, and by the remains from the 

 Eocene fresh-water deposits of the Western United States which 

 have been referred to the genera Boavus, Lithophis, and Limno- 

 phis. The genus Coluber is represented by several species from 

 the Miocene fresh-water deposits of the continent of Europe (Oen- 

 ingen, &c.). Fossil Toxicophidia, or venomous serpents, appear 

 to be still less abundantly represented than the non-venomous 

 types. A form supposed to be related to the rattlesnakes has been 

 described from Salonica as Laophis crotaloides, and one, related to 

 the cobra, from Steinheim, as Naja Suevica. The most ancient 

 remains of Ophidia in the New World appear to be those of Hela- 

 gras prisciformis, from the Puerco Eocene, which was of about the 

 size of the black constrictor (Coluber constrictor). 



The paucity of ophidian remains leaves very uncertain any specu- 

 lations as to the origin or evolution of this order of animals. 

 Whether or not they are in part the modified descendants of the 

 lacertilian pythonomorphs, which they seem to approximate in cer- 

 tain points of structure, still remains to be determined. 



Crocodilia. — Of the four orders of existing reptiles the Croco- 

 dilia are numerically the least important, and at the same time the 

 most restricted in their distribution. Some twenty-five more or 

 less well-defined species, inhabiting the tropical and sub-tropical 

 regions of the earth's surface, are known to naturalists, by whom 

 three distinct groups or families are recognised : the gavials, croco- 

 diles proper, and alligators. The gavials are exclusively Old World 

 forms, and the alligators forms belonging to the New World. The 

 * Palasophis littoralis, P. Halidanus, P. (Dinophis) grandis. 



