178 MR. D. M. S. WATSON ON 



Family Amphichelydice. 



Proganochelys Baur. U. Trias, Wiirttemberg. 

 Proterocherys E. Fraas. „ „ 



Super-Order SAUROPTERYGIA. 



Aquatic or semi-aquatic reptiles with a single temporal vacuity. 

 Neck long, the cervical ribs articulating solely with the centrum, 

 dorsal ribs single-headed. 



A single coracoidal element. 



Pelvis with an obturator foramen. 



Sub-Order Nothosauma. 



Semi-aquatic Sauropterygia. Paroccipital expanded and reach- 

 ing the squamosal, pterygoid, and quadrate so as to close the 

 middle ear behind. 



Radius and ulna, tibia and fibula long bones. 



Nothosaurus Minister. L. & M. Trias, Germany. 

 Cymatosaurus Fritsch. M. Trias, Germany. 



etc. 



Sub-Order Placodonta. 



9 



Sauropterygia with paroccipital not articulating with ptery- 

 goid and quadrate. Massive crushing teeth on the palatines. 

 (Body with a heavy armour of bony scutes.) Limb-bones long. 



Plaoodus Agassiz. M. Trias, Germany. 

 Cyamodus ,, ,, „ 



Placochelys Jaekel. „ Hungary. 



Order Thalattosauria Merriam. 



Aquatic reptiles with a single lateral temporal vacuity. A 

 supratemporal present. A single coracoidal element. Occipital 

 region of skull unknown. Humerus twisted with expanded ends. 



Thalattosaurus 1 Merriam. M. Trias, California and Nevada. 



Jyectosaurus 



Order Ichthyosauria. 



Aquatic reptiles with a single temporal vacuity, very large 

 orbits, and much elongated premaxilke. 



Basisphenoid without definite basipterygoid processes, ptery- 

 goids underlying much of its lower surface and that of the basi- 

 occipital. Neck short. 



Family Mixosaurlcle. 



Ichthyosauria with relatively small orbits and short rostrum. 

 Upper end of the scapula expanded. Pubis and ischium broad. 



