CRETACEOUS REPTILES. 397 
This indication has been since confirmed by the discovery of both teeth and 
vertebree of the Plesiosaurus in the same formation ; and the cervical vertebra 
figured in Tab. XL., which was obtained from the upper chalk-pit, at Houghton, 
near Arundel, Sussex, indicates a species nearly allied to the Plesiosaurus pachyo- 
mus from the greensand of Cambridge. 
The following are the dimensions of the vertebra from Houghton and of the 
most perfect of those of the above-cited species from the greensand :-— 
Pl. pachyomus. Pl. Bernardi. 
In. Lines. In. Lines. 
Longitudinal diameter of centrum. . . . 1 7 oe) 
Transverse Giametente evel. oy) ©. dilur ci, ateet nS 3 6°) 
Vertical diametetieaniiay «1.000 stn sued) onl 9 my AD 
The breadth of the centrum is proportionally greater in the vertebra from the 
chalk, which further differs from that from the greensand in the anchylosis of 
the pleurapophyses, pl (hatchet-bones or cervical ribs); which, if they presented 
the characteristic expansion of their extremities, must have supported the 
hatchet-shaped head on an unusually long body or pedicle. The articular 
surfaces of the centrum are more concave than in most Plesiosauri, and deepen 
to a central pit, in which they resemble those of the Plesiosaurus pachyomus ; 
but they differ inasmuch as the circumference of the surface is convex, and 
appears atc a,c p, upon a side view of the vertebra, fig. 3, Tab. XL. The 
central pit is transversely elongated in Pl. pachyomus, but is circular in Pl. Ber- 
nardi. 
Both neurapophyses (n) and pleurapophyses (pl) are anchylosed to the 
centrum. The neurapophyses coalesce together, and send almost vertically up- 
wards a spinous process which exceeds in length the whole vertical diameter of 
the vertebra below it, and is more than twice its own antero-posterior diameter ; 
it is compressed, and gradually decreases in thickness as it rises; it presents a 
rough shallow tract along its fore-part (fig. 1), and a deeper and smoother 
excavation behind (fig. 2, s). Two small zygapophyses (z, 2’) are developed 
from both the fore-part (z) and back-part (z') of the neural arch. The pleur- 
apophyses are long, subdepressed, slightly expanded as they extend downwards, 
outwards and backwards ; but the fractured ends do not show how far they 
have extended forwards and backwards into a hatchet-shaped extremity. They 
have coalesced with the lower part of the sides of the centrum, an extent more 
than their own vertical diameter intervening between them and the base of the 
3 F 
