Page:The Osteology of the Reptiles.pdf/277

Rh reptiles. Somewhat doubtfully associated with those remains are others of ichthyosaur-like bones that the describer provisionally associated with the Ichthyosauria, bearing possibly a like relation to the known Ichthyosauria that Globidens does to the typical Pythonomorpha.

Middle Triassic. Omphalosaurus Merriam, Nevada. Pessopteryx Wiman, Spitzbergen.

Quadrupedal, arboreal, terrestrial, or subaquatic reptiles one to six feet in length, with a single, upper temporal opening between the parietal and the temporal arch, the quadrate fixed. Ribs in part or all single-headed, articulating with centra—a single coracoid, an interclavicle, and clavicles.

This order, as here limited, is a provisional one, including several reptiles, some of them imperfectly known, which cannot be placed in any other known order. Most of them have hitherto been classified with the Rhynchocephalia, from which they are distinguished by the absence of a lateral temporal opening, so far as known. Perhaps when finally known they will be found to be incoherent. For the present they may be defined as families.

. Very slender, arboreal or leaping, hollow-boned reptiles of less than eighteen inches in length, with long legs and long tail. The broad lateral temporal region is formed apparently of a single bone, here identified as the squamosal, the quadratojugal absent. The dermosupraoccipital is apparently large. Lacrimal vestigial or absent. A parietal foramen. All cranial bones paired. Palatal bones with teeth. At least seven cervical vertebrae, twenty dorsal, two sacral, and a long, slender tail. Vertebrae amphicoelous with persistent intercentra. Cervical ribs, at least, single-headed, the dorsal more or less dichocephalous. Coracoid and scapula closely fused. Humerus with both entepicondylar and ectepicondylar foramina. Pelvis primitive. Phalangeal formula primitive. Calcaneum produced.

Araeoscelis, the type of the family, is the earliest definitely known reptile with a single, upper temporal vacuity, bounded as in the lizards, and a fixed quadrate. It was a very slender, leaping or