in North America of rare Extinct Vertebrates. 59 



the fin, decreasing in length from the radial, 54, to the ulnar, 55, 

 side, the fin of Leiodon resembles more that of the Cetacean* 

 than does the fin of Lestosaurus, but with the marked diffe- 

 rence of the first digit being the shortest in Cetacea and the 

 longest in the present genus of Mosasauria. 



The most instructive addition to the anatomy of this extinct 

 family of marine Saurians is the degree in which the dermal 

 skeleton is preserved in the Kansas example of Leiodon f. 



Prof. Marsh had referred certain dermal scutes to Mosa- 

 sauroid reptiles, and conceived them " to be mainly from the 

 lower part of the neck." " In the genus Liodon" he adds, 

 " the scutes are also imbricate, and somewhat similar to those 

 above described "J (in the genus Edesiosaurus) . But Prof. 

 Snow has brought to light an extensive series of such os- 

 seous scales, indicative of a more general dermal scutation. 

 Fig. 14, PI. VIII., is a copy of a portion of this armour 

 from one of the flanks of the Leiodon , of the natural size. 

 In no known Ophidian are the scales formed in any pro- 

 portion by bone ; the purely epidermal tissue of their exu- 

 vial coat would be wholly dissolved in remains from a 

 Cretaceous matrix, or, indeed, of one of more recent date. 

 The Sheppey and other Eocene serpents are represented 

 only by the parts of their endoskeleton ; and so large a 

 proportion of this has been found in natural articulation 

 as to lend ground for expectation that the dermal scales 

 would have been preserved if, as in lizards, they had included 

 petrifiable parts §. In the existing members of the Lacertian 

 order bone is developed at the base of the scale in several 

 genera, e. g. Trachysaurus, Tribolonotus, Ophisaurus 7 &c. 

 And if the curious fossils called " granicones," found in the 

 " Feather-bed " shales of the Middle Purbecks, have been 

 rightly interpreted ||, they likewise exemplify the osseous sup- 

 ports of the scales of an extinct lizard (Nuthetes destructor) — 

 and, by virtue of their tissue, have been susceptible of fossili- 

 zation, and testify to the dermal character of that species. 

 The formal character of both maxillary and mandibular 



* Quart. Journ. Geol. Soc. vol. xxxiv. p. 749, fig. 1. 



f " On the Dermal Covering of a Mosasauroid Reptile (Liodon dyspelor, 

 Cope)," by Prof. F. H. Snuw, op. cit. p. 54. The figure occupies p. 55. 



X 'Americau Journal of Science and Arts,' vol. iii. p. 11 (April 1872). 



§ Owen, 'History of British Fossil Reptiles,' 4to, p. 14G, pi. Ophidians, 

 4. I have lately been favoured, by Mr. Shrubsole of Sheerness, with an 

 opportunity of examining- a greater extent of the vertebral column of 

 Palcsophis toliapicus than the subject of my plate, but unaccompanied by 

 any trace of scutes. 



|| Transactions of the Royal Microscopical Society, vol. i. p. 233, 

 pi. xii. (1878). 



