FOSSIL VERTEBRATES — REPTILIA FAT 
perforation of the centrum, is absent in most of the Lacerta and 
all of the Ophidia. The loss of the limbs in the snake is but 
a secondary character, and is nearly accomplished in many 
genera of the lizards. 
The earliest of the Lacertilia is from the Isle of Purbeck in 
Dorsetshire, England. All that is known of the specimen are the 
imperfectly preserved remains of the skull and some of the scales. 
The genus is called Macellodon. 
Hydrosaurus, from the Lower Cretaceous of the Island of 
Lesina in the Mediterranean, was very similar in appearance to 
the modern monitors. (This genus was the direct ancestor of 
the great, specialized group of the Pythonomorpha developed dur- 
ing the Cretaceous. ) 
Dolichosaurus and Coniosaurus, from the Upper Cretaceous 
of England, and TZylosteus, from the Cretaceous of North 
America, are typical lacertilians. The Tertiary rocks of both 
hemispheres abound in the remains of the Lacertiia. The devel- 
opment of these forms began so early that even in the earliest 
Eocene we find representatives of the families and even of the 
genera of today. Zittel in his Handbuch enumerates from the 
Eocene of Wyoming the remains of Chameleo, [guanavus, Glypto- 
saurus, Saniva, Xestops, Thinosaurus, and Tinosaurus; from the 
Eocene Phosphorite (Upper Eocene) of Quercy, Agama, several 
genera of the Iguamde, Paleovaranus, and Lacerta. 
In the Miocene deposits of Europe are found many of the 
existing genera. In the Miocene of the western states, especially 
Colorado, are found such genera as Exostinos, Aciprion, Diacium, 
Platyrachis, and Crematosaurus. 
Most of the remains of the Pliocene and the Pleistocene forma- 
tions belong to existing genera and species, with the exception 
of the Australian Megalania and Notiosaurus. 
The Ophidia are very poorly known from the fossil forms. 
The only parts preserved are the vertebrae. With the single 
exception of Symoliophis, from the Cretaceous of Charente, the 
known fossils are from the Tertiary layers. From the London Clay 
(Eocene) and the Eocene sand of France come the remains of 
