{ 13. Amphicœla 13. Teleosauria * Teleosaurus IV. =Crocodiles= { 14. Opisthocœla 14. Steneosauria * Steneosaurus +Crocodilia+ { 15. Prosthocœla 15. Alligatores Alligator { 16. Sea tortoises 16. Thalassita Chelone V. =Tortoises= { 17. River tortoises 17. Potamita Trionyx +Chelonia+ { 18. Marsh tortoises 18. Elodita Emys { 19. Land tortoises 19. Chersita Testudo { 20. Long-tailed 20. Rhamphorhynchi * Rhamphorhynchus VI. =Flying= { Flying lizards =Reptiles= { 21. Short-tailed 21. Pterodactyli * Pterodactylus +Pterosauria+* { Flying lizards { 22. Giant dragons 22. Harpagosauria * Megalosaurus VII. =Dragons= { 23. Elephantine 23. Therosauria * Iguanodon +Dinosauria+* { dragons { 24. Dog-toothed 24. Cynodontia * Dicynodon VIII. =Beaked= { 25. Toothless 25. Cryptodontia * Udenodon =Reptiles= { 26. Kangaroo reptiles 26. Hypsosauria * Compsognathus +Anomodontia+* { { 27. Bird reptiles 27. 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.