Page:The Osteology of the Reptiles.pdf/254

236 broad, short, with large pineal opening, and palate and coronoids covered with conical teeth. Three sacral vertebrae. Texas.

Casea Williston, ? Trichasaurus Williston.

. Small, slender reptiles. Twenty-seven presacral vertebrae; three sacrals. Parasternal ribs present. Intimate structure of skull unknown. Skeleton feebly ossified, probably young animals, the metacoracoids not ossified. Vertebrae notochordal, ribs holocephalous. Lower Permian.

Paleohatteria Credner, Germany. Haptodus Gaudry, France. ? Callibrachion Boule, France.

. Mycterosaurus Williston, Glaucosaurus Williston, Tomicosaurus Case, Metamosaurus Cope, Embolophorus Cope, Texas. Archaeobolis Cope, Illinois. Aphelosaurus Gervais, Autun, France. Stereorhachis Gaudry (? Sphenacodontidae), Autun, France.

Doubtfully members of the order: Ammosaurus Huene (Triassic). Datheosaurus.

Less primitive, more upright-walking reptiles, the propodials more or less inclined in locomotion. Vertebrae amphicoelous, rarely notochordal, dorsal intercentra unknown. Palate and limbs less primitive; pelvis with larger pubo-ischiatic vacuity or thyroid opening.

As stated on a previous page, sharp distinctions between the members of this order and the preceding one cannot be made. The primitive characters common to both orders are largely included in the Synapsida. But the very great differences presented by the later, Triassic, forms, especially those included under the Cynodontia, differences as great as those between any other two orders of reptiles, render a division or divisions imperative, even though it may result, as is so often the case in other groups of animal and vegetable life, in the structural differences between members of the same group being greater than those limiting the groups themselves. This division, it seems to the writer, may be best made at the present time between the Lower and Middle Permian types, that is, based upon the stages of evolution chiefly. Perhaps when more is known