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 Primæval 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).

SYSTEMATIC SURVEY
Of the 8 Orders and 27 Sub-orders of Reptiles.
(Those groups marked with * became extinct even during the Secondary Period.)
Orders
of
Reptiles.		Sub-orders
of
Reptiles.		Systematic Name
of the
Sub-orders.		A Generic Name
as
an example.
I. Primary
Reptiles
Tocosauria

1.Primæval reptiles1.Proreptilia*(Proterosaurus?)
2. 2.Thecodontia*Palæosaurus
II. Lizards
Lacertilia

3.Cleft-tongued3.Fissilingues Monitor
4.Thick-tongued4.Crassilingues Iguana
5.Short-tongued5.Brevilingues Anguis
6.Ringed lizards6.Glyptodermata Amphisbæna
7.Chameleons7.Vermilingues Chamæleo
III. Serpents
Ophidia

8.Adders8.Aglyphodonta Coluber
9.Tree serpents9.Opisthoglypha Dipsas
10. 10.Proteroglypha Hydrophis
11.Vipers11.Solenoglypha Vipera
12.Worm serpents12.Opoterodonta Typhlops
IV. Crocodiles
Crocodilia

13.Amphicœla13.Teleosauria*Teleosaurus
14.Opisthocœla14.Steneosauria*Steneosaurus
15.Prosthocœla15.Alligatores Alligator
V. Tortoises
Chelonia

16.Sea tortoises16.Thalassita Chelone
17.River tortoises17.Potamita Trionyx
18.Marsh tortoises18.Elodita Emys
19.Land tortoises19.Chersita Testudo
VI. Flying
Reptiles
Pterosauria*

20.Long-tailed
Flying lizards		20.Rhamphorhynchi*Rhamphorhynchus
21.Short-tailed
Flying lizards		21.Pterodactyli*Pterodactylus
VII. Dragons
Dinosauria*

22.Giant dragons22.Harpagosauria*Megalosaurus
23.Elephantine dragons23.Therosauria*Iguanodon
VIII. Beaked
Reptiles
Anomodontia*

24.Dog-toothed24.Cynodontia*Dicynodon
25.Toothless25.Cryptodontia*Udenodon
26.Kangaroo reptiles26.Hypsosauria*Compsognathus
27.Bird reptiles27.Tocornithes*(Tocornis)

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 still living alligators are first met with in a fossil state in the chalk and tertiary strata. The most isolated of the four existing orders of reptiles consists of the remarkable group of Tortoises (Chelonia); fossils of these strange animals are first met with in the Jura. In some characteristics they are allied to Amphibia, in others, to Crocodiles, and by certain peculiarities even to Birds, so that their true position in the pedigree of Reptiles is probably far down at the root. The extraordinary resemblance of their embryos to Birds, manifested even at later stages of the ontogenesis, is exceedingly striking.

The four extinct orders of Reptiles show among one another, and, with the four existing orders just mentioned, such various and complicated relationships, that in the present state of our knowledge we are obliged to give up the attempt at establishing their pedigree. The most deviating and most curious forms are the Flying Reptiles (Pterosauria); flying lizards, in which the extremely elongated fifth finger of the hand served to support an enormous flying membrane. They probably flew about, in the secondary period, much in the same way as the bats of the present day. The smallest flying lizards were about the size of a sparrow; the largest, however, with a breadth of wing of more than sixteen feet, exceeded the largest of our living flying birds in stretch of wing (condor and albatross). Numerous fossil remains of them, of the long-tailed Rhamphorhynchia and of the short-tailed Pterodactylæ are found in all the strata of the Jura and Chalk periods, but in these only.

Not less remarkable and characteristic of the Mesolithic epoch was the group of Dragons (Dinosauria, or Pachypoda). These colossal reptiles, which attained a length of more than fifty feet, are the largest inhabitants of the land which have ever existed on our globe; they lived exclusively in the secondary epoch. Most of their remains are found in the lower cretaceous system, more especially in the Wealden formations of England. The majority of them were fearful beasts of prey (the Megalosaurus from twenty to thirty, the Pelorosaurus from forty to fifty feet in length). The Iguanodon, however, and some others lived on vegetable food, and probably played a part in the forests of the chalk period similar to that of the unwieldy but smaller elephants, hippopotami, and rhinoceroses of the present day.

The Beaked Reptiles (Anomodontia), likewise also long since extinct, but of which very many remarkable remains are found in the Trias and Jura, were perhaps closely related to the Dragons. Their jaws, like those of most Flying Reptiles and Tortoises, had become changed into a beak, which either possessed only degenerated rudimentary teeth, or no teeth at all. In this order, if not in the preceding one, we must look for the primary parents of the bird class, which we may call Bird Reptiles (Tocornithes). Probably very closely related to them was the curious, kangaroo-like Compsognathus from the Jura, which in very important characteristics already shows an approximation to the structure of birds.