KHYNCHUCEPHALIA. 18J) 



thick. The typical species is Hyperodapedo'u yordoni, perhaps about 

 two metres in length, known l>est by an imperfect skeleton from the 

 MI| 'posed Trias of Elgin. A larger species, H. huxleyi, is represented l>y 

 fragments in the Maleri Beds (supposed Trias) of Central India. 



Rhynchosaurus much resembles Hyperodapedon, but is comparatively 

 small, with fewer teeth, distinctly amphicoclous vertebra', and a longer 

 maims. Beautiful skeletons are found in the Upper Trias of Grinsill, 

 Shropshire. 



Homoeosaurus is the Jurassic representative of Sphenodon, from 

 which it differs essentially, (i.) in lacking intercentra or wedge-bones be- 

 tween the vertebral centra of the dorsal region, (ii.) in the absence of 

 uncinate processes to the ribs, and (iii.) in the humerus lacking its 

 entepicondylar foramen. Like the surviving genus, it has separated 

 external nares, toothed premaxilla 1 , the vertebral centra deeply biconcave, 

 and the rami of the mandible united at the symphysis only by ligament. 

 The typical species is H. maximiliani, known by nearly complete skele- 

 tons about - 2 m. in length, from the Lithographic Stone (Lower Kimrner- 

 idgian) of Bavaria. 



Champsosaurus. A large animal, representing a family of aquatic 

 Rhynchocephalia without dermal armour. The premaxillte are much 

 elongated into a gavial-like rostrum, and each bears a single series of 

 large conical teeth. The external nares are terminal and apparently 

 undivided. The hinder region of the skull, though imperfectly known, 

 is proved to have been Rhynchocephalian in plan, and the palate exhibits 

 the usual arrangement of its elements. The maxillae bear a single series 

 of large teeth ; the vomers, palatines, and pterygoids exhibit irregular 

 longitudinal series of comparatively small teeth. In the mandible, the 

 splenials enter the long symphysis, and there is no coronoid elevation. 

 The vertebral centra are slightly biconcave or have flat ends, and two 

 form the sacrum ; only two intercentra (hypocentra) or wedge-bones are 

 observed at the anterior end of the neck. The short cervical ribs are 

 double-headed. In the pectoral arch the interclavicle and clavicles are con- 

 spicuous; in the pelvic arch all three elements are considerably expanded 

 and enter the acetabulum. The humerus exhibits an ectepicondylar 

 groove at its distal end, but no foramen. The hind limb is a little longer 

 than the fore limb, and the digits in both must have been free or only 

 connected by a web. No angularly -bent median element has hitherto 

 been observed among the remains of abdominal ribs. Champsosaurus is 

 known not only by fragments from the Upper Cretaceous of the United 

 States, but by more nearly complete skeletons from the Lower Eocene of 

 Reims, France, and Erquelinnes, Belgium. 



