56 COPE 



Eibs two-headed ; interclavicle not dis- 

 tinct ; external digits greatly elon- 

 gate to support a patagium for 

 flight; (8) Ornithosauria. 



Ribs two-headed ; no interclavicle ; ace- 

 tabulum open ; ambulatory ; (9) Dinosauria. 



Ribs two-headed ; an interclavicle ; ace- 

 tabulum closed ; ambulatory ; (10) Loricata. 



Ribs one-headed ; an interclavicle ; ace- 

 tabulum closed, a large obturator 

 foramen ; ambulatory ; (11) Rhynchocephalia. 



II. Quadrate bone loosely articulated to the cranium 

 and at the proximal end only. (Streptostylica). 



No distinct supramastoid, nor opisthotic ; 

 one or no postorbital bar; scapular 

 arch external to ribs when present ; 

 ribs one-headed ; (12) Squamata. 



It appears that four orders are Paleozoic in age, one of 

 which possibly continues into the Trias (Theromora). 

 Four are exclusively, Mesozoic, while four continue to 



exist. 



The Theromora present the greatest resemblances to the 

 Mammalia, while the Cotylosauria present resemblances to 

 the Stegocephalian Batrachia with which they agree essen- 

 tially in the structure of the temporal roof, in the presence 

 of the tabular and supramastoid bones. 



The three plates which follow present diagrams of dorsal and lateral views of 

 all of the orders of Reptllia except the Chelydosauria. The bones are indicated by 

 a uniform system of abbreviations. — Ed. 



