12 
FOSSIL REPTILIA OF THE 
Plesiosaurus liomalospondylus (Tabs. V — VIII). 
In the year 1842 I examined, in the Museum at Whitby, Yorkshire, a collection of 
Plesiosaurian vertebrae, which had been taken out of a heap of rubbish from the old 
alum works carried on in the upper Alum Shale — a part of the Liassic series on that 
coast, characterised by the Ammonites heterojjhyllus, Sow. 
The vertebrae were divisible into two groups, indicative of two species of 
Plesiosaurus. 
Of one kind there was a series of sixteen consecutive cervical vertebrae, charac- 
terised by the unusual concavity of the terminal articular surfaces of the centrum. On 
making a section of two of these vertebrae cemented by the matrix in their natural 
state of co-adaptation, the margins of the opposed articular surfaces were two lines 
apart, showing the thickness of the inter-articular connecting ligamentous substance at 
that part, while the middle of the articular surfaces left an interval of eleven lines, thus 
approaching the ichthyosaurian type of vertebral union. 
The following w^ere dimensions of the centrum of these cervicals. 
In. lines. 
Length .......... 19 
Breadtli of articular surfaces . . . . . . Ill 
Height of ditto . . . . . . . . . 110 
The inferior surface of the centrum showed a median longitudinal convex ridge 
between the two wide elliptical venous foramina. I named the species indicated by 
these vertebras Plesiosaurus coelospondylus* in reference to the hollow terminal articular 
surfaces. I hope to have, at a future opportunity, further means of illustrating this 
species. 
The second series of vertebrae presented almost flat articular surfaces of the centrum 
(Tab. V, figs. 3 and 6) ; the inferior surface w^as devoid of a median ridge, or had only 
a slight rising (fig. 4, v) between the venous foramina, which w’ere smaller and more 
narrowly elliptical (ib., figs. 4 and 7) than in PL ccelospondylus \ the middle of the 
surface was bounded laterally by the costal surfaces pi), and was nearly flattened, 
being very slightly concave, both lengthwise and transversely. The costal surface is 
of a narrow elliptical form, with the long axis parallel wnth that of the centrum ; the 
dividing line or fissure is not conspicuous ; it is situated, as usual, rather nearer the 
back than the front end of the centrum (Tab. V, fig. 2, pi) ; and a space more than 
twice its vertical diameter intervenes between it and the neurapophysis (ib., np), or 
* KoiXos, hollow, airot bvXos, vertebra. 
