Mr. IT. Sccley on two new Plesiosaurs from the Lias. 353 



dicatc a young animal ; but, though probably not aged, there is 

 no evidence that it was immature. 



The species hitherto undetermined, indicated by twenty-four 

 vertebras between the last of the neck and the first of the tail, 

 and by eight carpal bones and five bones in the tarsus, is 

 different from every other yet characterized. So it will now be 

 described as 



Plesiosaurus eleutheraxon *. 



The atlas and axis are contrasted with the same bones in Plesi- 

 osaurus Etheridyii, and well figured in the ' xlnnals of Natural 

 History' for November 1858. To these succeed eleven verte- 

 bras, which with their interspaces occupy 9f inches. The para- 

 pophyses for the hatchet bones occupy at first all the width be- 

 tween the epiphyses, but at the thirteenth they are found only 

 on the hinder half of the side of the vertebras. The neura- 

 pophyses soon extend to the whole length of the vertebras ; the 

 zygapophyses are long, the neural spine compressed, wide, and 

 not very high. The sides of these cervical vertebras are flat- 

 tened, but the under surface between the hatchet bones is exca- 

 vated. 



The third vertebra is -p- inch long, and § of an inch wide 

 over the articular end, which is -fe of an inch high. Subsemi- 

 circular in outline in front, being flattened above, it is moderately 

 concave, and, like all the cervical vertebras, has a bevelled border, 

 which is always of the same width. The articular surface is 

 oval in the sixth, which is nearly |- of an inch wide and -f- high. 

 The thirteenth is ^ of an inch long. 



Two inches' interspace here separates the next, three vertebras, 

 which are noticeably larger, have long narrow venous foramina 

 between the small ploughshare bones, and extend over 3| inches. 

 The last of these vertebras measures 2| inches from base to top 

 of the neural spine, which is much less high in front than be- 

 hind, and from front to back nearly as long as the vertebra. 



After these there is a vacant interspace of 11 inches; and 

 then the remainder of the spinal column is continuous to the 

 end, the thirty-five vertebras maintaining a nearly uniform size. 



In the first seven the circular parapophysis rapidly ascends the 

 side, becoming elliptical, and at the eighth the articulation for the 

 rib, which there becomes very much larger, is entirely supported 

 on the neural arch. The sides are concave, so that the epiphyses 

 form a broad rim, and inferiorly they meet in a sharp angle, 

 which disappears with the first dorsal. The seven vertebras 

 measure 10 inches. The neural spine is now much longer, and 

 makes the height of the first of these seven cervicals 3,' inches. 



* eXevdepos, Lat. liber; u^a>v, Lat. axis. 



Ann. $ Mag. N. Hist. Ser. 3. Vol. xvi. 24 



