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Mr. E. S. Goodrich. 



Chelonia. — Opinions as to the affinities of the Chelonia have been widely 

 divergent. Palaeontology affords little or no evidence concerning the origin 

 of this very isolated and specialised order. While some authors have pointed 

 out resemblances to the Khynchocephalia, Baur (1) and others have held that 

 they are related to the Sauropterygia. Jaekel (19) has derived them from 



Fig. 4. — Diagrams of the Heart and Aortic Arches of an Amphibian (A), a Mammal (B), 

 a Reptile (Chelonia. Lacertilia, Ophidia, Khynchocephalia) (C), and a Crocodile (D) ; 

 ventral view. The heart is represented as untwisted so as to bring the chambers 

 into a single plane, with the sinus venosus behind and the ventricle in front. 

 B, transverse section through region of the bulbus cordis ; T, transverse section 

 through the truncus arteriosus ; d, ductus Botalli ; ec, external carotid ; ic, internal 

 carotid ; la, left auricle ; ha, left systemic arch ; Iv, left ventricle ; p, pulmonary 



Placodontia ; but most recent writers prefer to derive them independently 

 from some primitive Cotylosaurian ancestor, owing to the absence of true 

 foramina in the temporal roof of the skull. Now the structure of the foot, 

 provided with the characteristic hook-shaped metatarsal, and of the heart 

 built on the Sauropsidan plan, clearly show that the Chelonia belong to the 



