Page:The Osteology of the Reptiles.pdf/230

212 1. PARAPSIDA. A single temporal opening, between parietal and postorbito-squamosal arch; supratemporal (tabular) persistent. Ribs articulating more or less exclusively with centrum. A single coracoid.

1. Proganosauria. Skeleton largely primitive. Aquatic, the neck and tail elongate. Phalangeal formula 2, 3, 4, 5, 4 (6). Skull imperfectly known; the quadrate fixed. Lower Permian.

2. Ichthyosauria. Marine reptiles with short neck and all aquatic adaptations. Vertebrae amphicoelous; no dorsal intercentra. Quadrate fixed. Middle Triassic to Upper Cretaceous.

3. Protorosauria. Aquatic or terrestrial. Not more than seven cervical vertebrae. Vertebrae amphicoelous (? Saphaeosauridae). Quadrate fixed. Phalangeal formula primitive. Lower Permian to Jurassic.

4. Squamata. Quadrate freely articulated proximally (streptostylic) or secondarily fixed.

1.

2. (Sauria). Parietals never united to basisphenoid by descending plates, the brain-case more or less membranous anteriorly.


 * (a) Kionocrania. An epipterygoid present ; vertebrae amphicoelous with persistent dorsal intercentra, or procoelous and no dorsal intercentra; eight cervical vertebrae; limbed or limbless. Phalangeal formula primitive. Cretaceous to Recent.


 * (b) Platynota. An epipterygoid. Vertebrae procoelous. Nine or more cervical vertebrae. Phalangeal formula primitive. Lower Cretaceous to Recent.


 * (c) Pythonomorpha. Marine reptiles; limbs paddle-like, hyperphalangic; seven cervical vertebrae, procoelous; an epipterygoid present. Upper Cretaceous.


 * (d) Amphisbaenia. No epipterygoid or temporal arch, the quadrate secondarily fixed; limbless or with vestigial front legs; vertebrae procoelous. Oligocene to Recent.


 * (e) Rhiptoglossa. No epipterygoid or clavicles ; five cervical vertebrae; vertebrae procoelous; phalangeal formula 2, 3, 4, 4, 3. Oligocene to Recent.

3. (Serpentes). Brain-case enclosed by descending plates from parietals and frontals; no epipterygoids; no temporal arch; mandibles united by ligament. Vertebrae procoelous, with zygosphenes; no chevrons. Limbless. Cretaceous to Recent.

2. DIAPSIDA. Two temporal openings, separated by postorbito-squamosal arch; no supratemporals or tabulars (? Youngina). A