On the Classification of the Reptilia. 



267 



has hitherto been very uncertain, and in which the structure of the skull 

 fails to yield decisive evidence. 



Mesosauria (Proganosauria). — The very ancient fossils, Mesosaurus tenuidens, 

 Gervais, from South Africa, and the closely allied Stereostemum tumidum, 

 Cope, from South America, were placed in a new order Proganosauria by 

 Baur (1), who believed them to be related to the Ehynchocephalia. Osborn 



Fig. 3.— Skeleton of the Hind Foot of :— A, Palceohatteria longicaudata, Cr., from 

 Credner (14) ; B, Procolophon, from Watson (33) ; C, Naosaurus, from Osborn (27) ; 

 D, Mesosaurus (Stereosternum), from a specimen in the British Museum ; E, 

 Pleurosaurus goldfussi, H. v. M., from Lortet (21 ) ; F, Lariosaurus, from Boulenger (6). 

 All, except E, are somewhat restored. 



included them in the Diapsida (26) ; and in a more recent paper, McGregor, 

 (23), on what appear to be very insufficient grounds, claimed that 

 Mesosaurus has a skull with two temporal fossee, and is allied to the 

 Ehynchocephalia and Protorosauria (including Palaeohatteria). He denies 

 the affinity with the Plesiosauria upheld by Seeley (29), and afterwards so 

 well supported by Boulenger (6). Williston refuses to commit himself (34), 

 but inclines to the view that the Mesosauria are allied to the Theromorpha, 

 vol. lxxxix. — B. z 



