Page:The Osteology of the Reptiles.pdf/282

264 elongate, pointed, the nares remote from end. No postfrontals. A parietal foramen. The single temporal opening is bounded within by the parietal, without by the postorbital and (?) squamosal. A small quadratojugal. Teeth pointed and recurved. Acrodont. Palatal teeth unknown. Five cervicals, forty or forty-one dorsals, two sacrals, and more than seventy caudals. Vertebrae amphicoelous, cervical intercentra hypapophysial. Ribs single-headed, articulating as in the Squamata. Numerous slender, parasternal ribs.

Pleurosaurus, the only certainly known genus of the family, was long supposed to be a member of the Rhynchocephalia, though it has also long been known to have but a single upper temporal opening. Its remarkable adaptation to aquatic life is shown in the elongated head, posterior nares, short neck, very slender trunk, very small legs, and enormously elongated tail, with its long chevrons and spines, which in life was surmounted by a thin crest of scales.

Acrosaurus is probably only the young of Pleurosaurus, as the author convinced himself by examination of specimens in the Munich museum. In consequence, the ordinal name once proposed for these reptiles, Acrosauria, is inappropriate. The structure of the temporal region still needs confirmation. If there is but a single bone bounding the temporal opening posteriorly, it is in much probability the real squamosal.

Uppermost Jurassic. Pleurosaurus v. Meyer (Anguisaurus Münster, Saurophidium Jourdan), Germany, France. ? Acrosaurus v. Meyer. Germany.

With a single temporal vacuity on each side, bounded by parietal, tabular, squamosal, and postorbital, secondarily sometimes roofed over or the arcade obsolete. No lower temporal opening or bar. Quadrate movably articulated, streptostylic, secondarily sometimes fixed. No supratemporals, dermosupraoccipitals, or quadratojugals. The pterygoids articulate in front with the palatines, never with the prevomers. Paroccipitals fused with exoccipitals. Interorbital septum not ossified. Teeth acrodont or pleurodont, often attached to palatine and pterygoid. Prearticular fused with articular. Ribs single-headed, articulating with centrum.