Superorder DIAPTOSAURIA. 



Onlci- THALATTOSAIHIA.' 



Mariin' snuriaiis with a Khi'cvia t (■<! prdpodial a n d c [>i pod i a 1 liiiil) 

 segments, eloiigatcil facial rcuion, and nnMliaii cxtcrual narcs. 

 Slvull with superior and lateral temporal opeiiiiins and a pineal 

 foramen. I'revomers and pterygoids as well as jaw elements 

 dentigerous. General structure of skeleton of the rhynchoceph- 

 a 1 i a 11 t y [) e . 



The group is eonnioseil of specialized natatory forms known only from 

 marine deposits. It stands in somewhat the same rcdation to the typical 

 Rhynohoeephalia as tliat which the Mosasauria hear to the Lacertilia. 

 Evidently derived from a primitive land or shore 1 )iaptosauriaii, it has taken 

 somewhat the same course in evolution as was foUoweil later hy the Mosasaurs. 



Family TllA LATTUSAURIDAE." 



Skull elongated, with slender rostrum. External iiares sepa- 

 rate and not far in front of the or hits. I'rema x i 11 a ries elongated 

 and forming a large portion of the snout. I'reni a x i 1 1 a ries, maxil- 

 laries an<l dentaries sculptured on external surface. Superior 

 and lateral temporal openings and pineal opening present. 



I'revomers with two rows of heavy. low-croAvned teeth. Ptery- 

 goids with four or more rows of curved conical teeth. Prema \il laries 

 and anterior end of dentary with slender conical teeth. Posterior 

 part of dentary generally with de[)ressed or iiattened teeth. 



Vertebrae amph icoel ous, neural spines generally high and 

 slender. Dorsal rihs single-headed. Abdominal riiis present. 

 Coracoid reniform, elongated a n t ero-posterior ly. Scapula narroAV. 

 Humerus short, expanded distally. Radius and ulna about half 

 the length of , the humerus; radius with median constriction; 

 posterior border of ulna convex, radial border concave. 



OCCURRENCE AND AGE. 



The material upon which the group descrilu'il in this paper has been 

 based was all obtained in exposures of the Hosselkus Limestone lying between 

 Squaw C'reek and Pitt River, in the northern part of Shasta County, California. 



1 J. C. MeiTiam, Bull. Dept. Geol. Univ. Calif, v. :f, no. 21, p. -12U. 



2 IbUi. 



