160 REPORT OF NATIONAL MUSEUM, 1898. 



aa Scapular and pelvic art-hes within tlioracic and aljdoniinal bouea. 



A paroccipital; iio supramastoid; a large proscapula, no precoracoid, 

 coracoid free from Bternuni behind; ribs one-headed, interceu- 

 tral Testudinata. 



III. Quadrate immovably articulated; two postorbital bars (Archosauria). (No par- 



occipital bone.) 

 Ribs two-headed; no interclavicle; external digits greatly elongated to 



support a patagium; a distinct pectineal bone Ornithosauria. 



Ribs two-headed; no interclavicle; acetabulum perforate at middle of 



ilium; feet ambulatory Dinosauria. 



Ribs partly two-headed; an interclavicle; acetabulum closed; feet 



ambulatory ; no pectineal bone Loricata. 



Ribs one-headed; an interclavicle; no pectineal bone; acetabulum 



closed ; feet ambulatory Rhynchocephalia. 



IV. Quadrate bone loosely articulated, and at proximal extremity only ; one or no 



postorbital bar [Streptostijlica). 

 a A paroccipital bone. 



Ribs ono-headed; no pectineal bone; acetabulum closed; feet 7iot 

 volant Squamata. 



Of these orders, five are extinct and four still exist. Their afftnities 

 and time relations may be expressed by the following table. The ver- 

 tical lines represent duration in geologic time. 



Plistocene 

 Neocene 



Eocene 



Post 

 Cretacic 



Cretacic 

 Jurassic 

 Triassic 



Carbonic 



Demonic 



5/LUR/C 



HURONIC 



Laurent/ c 



Ornithosauria 



Plesiosaurja 



Squamata 



JchthyoptehygiA Testudinata 



Cotylosauria 



