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CHAPTER IV. 



Order— ENJZIOSA UBIA. 



Genus. — Plesiosaurus, Conyleare. 



Besides the teeth which, according to their form and structure, were referable to 

 the different genera and species of Iteptilia above described, — viz. to Baphiosatcrus, 

 (PI. 9, fig. 2;) to Coniosaurus, (PI. 2, fig. 19a;) to Mosasaurus, (ib., fig. 1;) to Leiodon, 

 (PI. 10, fig. 1 ;) and to Poli/pti/chodon, (' Crocodilia,' PL 26 and PI. 29,)— we now, for the 

 first time, in our progressive researches, descending through the strata which indicate 

 the changes which the part of the earth's surface, forming England, has undergone, 

 meet with teeth of different and peculiar type, remarkable, viz., for their length and 

 slenderness, and with a circular transverse section, not subcompressed or with opposite 

 trenchant margins, as in the Gavials of the Tertiary deposits. The tooth represented 

 of the natural size in PI. 2, fig. 8, is a good example of one of those of the form in 

 question. Its enamelled crown, if entire, would exceed an inch and a half in length, 

 yet it is but half an inch in diameter at its base ; the crown is slightly curved 

 and tapers gradually to a point ; the enamel presents some slender but well-defined 

 longitudinal ridges of different lengths, and none of them extending to the apex. The 

 fang or root is cylindrical, smooth, and covered by a thin cement. The tooth above 

 described was obtained from the Scaddlescombe Chalk-pit, near Lewes, Sussex. 



A similar specimen, rather more fractured, PL 2, fig. 9, was found in a Chalk-pit at 

 Southeram, Sussex. 



A smaller tooth, (PL 2, fig. 13,) of the same type, but with more numerous longi- 

 tudinal ridges, seems to indicate a different species. This specimen was also found 

 at Southeram. 



If satisfactory and abundant evidence of the nature of the extinct reptile to which 

 the above-described teeth belong had not been obtained from Secondary Formations of 

 a more ancient date than the cretaceous ones, the Comparative Anatomist would have 

 inferred, and correctly, the generic distinction of the Reptile to which they belonged ; 

 but he could have had no suspicion of the truly extraordinary nature ctf the animal, the 

 entire race of which, after flourishing under a variety of specific forms from the epochs 

 of the Muschelkalk and Lias, finally perished at the time of the deposition of the 

 Chalk. 



The anatomical description of the Plesiosaurus, discovered and restored by 

 CoNYBEARE and De la Beche, will be reserved for the Monograph descriptive 

 of the fossil Reptiles of the formations in which its remains are most abun- 



