THE SUBCLASS SYNAPTOSAURIA 251 



Family Brachaucheniidae. Skull long, neck very short, with but 

 thirteen vertebrae, shorter than skull. Cervical ribs singleheaded. 

 Pterygoids not reaching to vomers. Paddles imperfectly known. 



Upper Cretaceous. Brachaiicheniiis Williston, North America. 



Genera incertae sedis 



Triassic. ^'Plesiosaurus" Conybeare, Europe. 



Jurassic. Eretmosaurus Seeley, Colymhosaurus Seeley, Ischyrodon 

 Meyer, Lioplenrodon Sauvage, Spondylosaiirus Fischer, Simolestes 

 Andrews, Europe. M egalneusaurus Knight, Pantosauriis Marsh, 

 " Muraenosaurus^' Seeley, North America. 



Lower Cretaceous. " Plesiosaurus^' Conybeare, North America. 



Upper Cretaceous. Mauisaurus Hector, New Zealand. Polypty- 

 chodon Owen, Europe. Cimoliosaurus Leidy ,OligosimusL,eidy , Brimo- 

 saurus Leidy, Pi ptomerus Cope, Orophosaurus Cope, Embaphias Cope, 

 Taphrosaurus Cope, Uronautes Cope, ^^ Plesiosaurus^' Conybeare^ 

 North America. 



7. ORDER PLACODONTIA 



Temporal opening bounded by parietal, postfrontal, postorbital, 

 and squamosal. Jaws and palatines with few, very large, flat crush- 

 ing teeth. A parietal opening. Vertebrae amphicoelous, with hypo- 

 sphene, hypantrum. Ribs double-headed. Remainder of skeleton 

 unknown. 



This singular group of littoral, shell-eating reptiles has long been 

 a problem, because of our ignorance of the skeleton. Some would 

 include them among the Sauropterygia as a separate suborder; 

 others would give to them the same rank among the Therapsida. If 

 the supratemporal and interparietal are really present, as believed 

 by Huene, they would certainly find no place among the Sauro- 

 pterygia. But their presence has been denied. On the other hand, if 

 there should prove to be but a single coracoid on each side in the 

 pectoral girdle, their location among the Therapsida would be im- 

 proper. Placochelys has a carapace of bony plates, both above and 

 below, with isolated ones upon the skull, all of which seem to be 

 wanting in Placodus. Their presence or absence, however, is of no 

 more importance than in the Dinosauria, or Squamata, as examples. 



