154 BRITISH FOSSIL REPTILES. 



so far from the type-characters of Plesiosaurus as to merit being placed in a 

 distinct genus or subgenus, for which I proposed the name of Pliosaimis ; admitting 

 at the same time in reference to the two species, that " subsequent discoveries and 

 observations were needed to supply distinct and recognisable characters for them " 

 — " the two forms of femora, on which they were founded, not having then been 

 found so associated with vertebrae and other bones as to aid in their definition." ^ 



I am now enabled to describe and figure specimens, among those that have 

 subsequently come under my notice, which afford good grounds for the acceptance 

 of the two species, and for the addition of a third to the genus Pliosaurus. It may 

 seem strange that jaws which have lost all their teeth should yield new characters 

 derivable from the number, proportions, and disposition of such organs ; but herein 

 a Paleontologist's mode of work is like that of Antiquaries of another order, 

 who read inscriptions on Roman buildings by the nail-marks when the letters 

 themselves have been wrenched off for the sake of the metal. 



Species — Pliosaurus grancUs, Owen (Sauropferygia), Plate 19, figs. 1 and 2. 



PLESiosATJErs OEANBis, Ow. Eepopfc on British Fossil Eeptiles, 8vo, p. 83, 1839. 

 PLiosAUErs BEACHTDEiEUs, Ow. Odontography, 4to, p. 283 (?), 1840. 



The most complete example of the skull of a Pliosaur which has come under 

 my observation was disinterred from the Kimmeridge Clay, at Kimmeridge, 

 Dorsetshire, under the superintendence of J. 0. Mansel-Pleydell, Esq., F.G.S., of 

 Longthorns, in that county. This skull is also the largest of such specimens 

 hitherto found ; and, since the matris has been removed, it has yielded the most 

 instructive chai^acters of cranial structm^e and dentition. Originally sent to me 

 with the skull of Plesiosuchus (p. 147, pi. 20) for determination and description, 

 both specimens have since been presented by their discoverer to the British 

 Museum. The same liberal donor has subsequently enriched the National Collec- 

 tion by a lower jaw and part of the cranium, with evidence of the locomotive 

 organs of the Pliosaurus trochanter ius. I shall premise to the descriptions some 

 of the dimensions of remains of both specimens. 



1 lb. (Second Keport), p. 54, 1841. 



