300 SATJROPTEEYGIA. 



Family MESOSAURIMl. 



Skull long and slender, but its palatal structure unknown. 

 Vertebrae with a notochordal canal and relatively small centra, 

 apparently of the same general structure as those of the Notlio- 

 sauridce. Bibs very thick and apparently anchylosed to the vertebrae. 

 Pectoral and pelvic girdles and limb-bones of the general type of 

 those of the latter ; five distinct tarsalia in pes, of which the fifth 

 digit is the longest. The structure of the pes would seem to indicate 

 a webbed foot like that of Progs. 



The so-called Stereosternum, on account of the presence of five bones 

 in the distal row of the tarsus, has been made by Baur (' Morphol. 

 Jahrb.' vol. i. p. 103, 1887) the type of a distinct order, under the 

 name of Proganosauria ; there can, however, be no question but that 

 such a character cannot be allowed to outweigh its manifest affinity to 

 the Noihosauridce {vide Seeley, ' Phil. Trans/ 1888, pp. 104, 105). 



Genus MESOSAURUS, P. Gervais \ 



Syn. Stereosternum, Cope 2 . 



The type and only known genus, Stereosternum presenting no 

 characters by which it can be distinguished 3 . 



Mesosaurus tenuidens, P. Gervais 4 . 



The type species. Length of mandible 0,064 (2*53 inches), and 

 of humerus 0,026 (1-02 inches). The size of the entire animal is 

 approximately the same as that of SjpTienodon. 



Hah. South Africa. 



49659. A cast taken from a slab of shale showing the impression of 

 the ventral aspect of the anterior half of the skeleton. 

 The original specimen is the type, and was obtained from 

 the Karoo system (probably Lower Mesozoic) of Griqua- 

 land West, and is preserved in the Paris Museum. The 

 cast in relief is figured by P. Gervais in his ' Zool. et Pal. 

 Generales,' ser. 1, pi. xlii., and the left pectoral limb in 

 the accompanying woodcut. The skull and both pectoral 

 limbs are well preserved, but the characters of the pec- 



1 Zool. et Pal. Generates, ser. 1, p. 223 (1867-69). 



2 Proc. Amer. Phil. Soc. vol. xxiii. p. 7 (1886). 



3 The detached coracoid figured by Cope, op. cit. pi, i. fig. 8, must belong to 

 a different reptile. 4 Log. cit. 



