264 THE OSTEOLOGY OF THE REPTILES 



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 sa- 

 crals, and more than seventy caudals. Vertebrae amphicoelous, cer- 

 vical 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 Miin- 

 ster, Saurophidium Jourdan), Germany, France. ? Acrosaurus v. 

 Meyer. Germany. 



11. ORDER SQUAMATA 



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 sep- 

 tum not ossified. Teeth acrodont or pleurodont, often attached to 

 palatine and pterygoid. Prearticular fused with articular. Ribs 

 single-headed, articulating with centrum. 



