Mr. H. Seeley on two new Plesiosaurs from the Lias. 353 



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

 no evidence that it was immature. 



The species hitherto undetej'mined, indicated by twenty-four 

 vertebrse 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 Etheridgii, and well figured in the ' Annals of Natural 

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

 brse, which with their interspaces occupy 9|- 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 vertebrse. The neura- 

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

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

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

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

 vated. 



The third vertebra is -^ inch long, and | of an inch wide 

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

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

 concave, and, like all the cervical vertebrse, 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 -f of an inch long. 



Two inches' interspace here separates the next three vertebrse, 

 which are noticeably larger, have long narrow venous foramina 

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

 The last of these vertebrse 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 1 1 inches ; and 

 then the remainder of the spinal column is continuous to the 

 end, the thirty-five vertebrse 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 vertebrse 

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

 makes the height of the first of these seven cervicals 3^ inches. 



* eXevdtpos, Lat. liber ; a^av, Lat. axis. 

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



