RECENT AND FOSSIL REPTILES, 223 
Gymnosperms (p. 111). Twelve of the twenty-seven sub- 
orders, given on the accompanying table, and four of the 
eight orders, belong exclusively to the secondary period. 
These mesolithic groups are marked by an asterisk. All 
the orders, with the exception of Serpents, are found fossil 
even in the Jura and Trias periods. 
In the first order, that of Primary Reptiles, or Primary 
Creepers (Tocosauria), we class the extinct Thecodontia of 
the Trias, together with those Reptiles which we may look 
upon as the common primary form of the whole class. 
To the latter, which we may call Primeval Reptiles 
(Proreptilia), the Proterosaurus of the Permian system 
very probably belongs. The seven remaining orders 
must be considered as diverging branches, which have 
developed in different directions out of that common 
primary form. The Thecodontia of the Trias, the only 
positively known fossil forms of Tocosauria, were Lizards 
which seem to have been like the still living monitor 
lizards (Monitor, Varanus). 
Of the four orders of reptiles now existing, and which, 
moreover, have alone represented the class since the 
beginning of the tertiary epoch, that of Lizards (Lacertilia) 
is probably most closely allied to the extinct Primary 
Reptiles, and especially through the monitors already 
named. The class of Serpents (Ophidia) developed out of a 
branch of the order of lizards, and this probably not until 
the beginning of the tertiary epoch. At least we at 
present only know of fossil remains of serpents from the 
tertiary strata. Crocodiles (Crocodilia) existed much earlier ; 
the Teleosauria and Steneosauria belonging to the class are 
found fossil in large quantities even in the Jura; but the 
