THE REPTILIAN CLASS OF THE MOSASATJRID^:. 713 



Triassic Reptilia of South Africa. Some of these now lacertian 

 peculiarities, combined with ichthyo- and plesio-saurian ones, are 

 carried on to Cretaceous times. Between the orders manifesting 

 such combinations and the Mosasaurians, links are, indeed, still 

 wanting; but so much as is now known, fragmentarily, of the 

 Cretaceous Polyptychodon, indicates one of the transitional steps. 

 The portion of skull, at least, which is figured in t. iv. fig. 1 of 

 the Monograph of Cretaceous Heptilia, in the volume of the Palaeon- 

 tographical Society for ]860, shows the lacertian hinder bifurcation 

 of the parietal, the articulation of the long prongs with the 

 mastoids, and of the mastoid with the posterior part of the long, 

 upper, slender zygomatic arch. The foramen parietale, more- 

 over, is exhibited, and under the Amblyrhynchian modification, viz. 

 its perforation at the suture between the parietal and frontal 

 bones. 



In not one of the steps by which, in those old and more or less 

 generalized reptilian forms, purely lacertian are associated with 

 crocodilian or chelonian characters, and with others that have passed 

 away, is there a single strictly or truly ophidian modification. I 

 have sought for such in vain in the evidences of the Mosasaurians, 

 where the lacertian characters predominate ; and when these are 

 departed from, as in the simplification of the neural arch through 

 loss of the zygapophyses, in vertebrae beyond the middle of the 

 trunk, the great Cretaceous Sea-lizard looks whaleward rather than 

 snakeward. 



If I were to hazard a guess as to any antecedent form leading 

 toward the earliest certainly known Ophidian, viz. the pythonic 

 and perhaps marine forms of the Eocene period, it would be the 

 DoMchosaurus of the white Chalk of Kent that would suggest itself. 

 In this extinct form as many as 57 vertebras appear to have inter- 

 vened between the skull and the sacrum. But the sacrum exists, 

 and there are likewise scapulas and humeri. The vertebrae, more- 

 over, as in Mosasaurus, retain the lacertian character of zygapo- 

 physes and of the absence of the hypapophysis in the anterior and 

 succeeding trunk-vertebrae. 



No true ophidian characters have been found in any fossils indi- 

 cative of a serpent exceeding in size the largest of the Constrictors ; 

 and these existing giants of the ophidian order are terrestrial. The 

 average length of the existing Sea-serpents (Hydrophidae) is 3 feet ; 

 and the experienced herpetologist, Dr. Gunther, P. U.S., informs me 

 that he has seen no specimen of the family which exceeded 8 feet 

 in total length. 



But the Lacertian modification of the reptilian class continued to 

 be represented as lately as the drift-period in Australia by a genus 

 (Megcdania) * of which I have now before me dorsal vertebrae 

 measuring 5 inches 2 lines in transverse diameter, 5 inches 9 lines 

 in vertical diameter. A comparison of such vertebrae with the ad- 



* Phil. Trans. 1858, p. 43, pi. vii. 

 t Op. cit. pp. 135 and 137. 



