THE CAMBRIDGE GREENSAND, 601 
the external alveolar wall is higher than the inner wall, and ap- 
pears always to have been higher. In the length of 27 inches are 
the sockets or spaces for thirteen teeth; the sockets appear to have 
been nearly half an inch deep, and parallel to the inner surface of 
the jaw, so that the teeth were directed outward. The sockets were 
apparently nearly circular; but owing to this outward direction 
they appear as though they were transversely oblong. The inner. 
surface of the jaw is approximately parallel to the outer surface ; 
it consists of two areas—a long flat superior space, the plane of which 
is twisted a little outward anteriorly, about 2 inch deep, and limited 
inferiorly by a sharp straight angular ridge; and below this is a 
channel attenuated anteriorly, the side of which bends under the 
superior area(see Pl. XXXV. fig. 1 a). The thickness of the bone be- 
comes reduced below the ridge, being hardly more than 4 inch thick 
where fractured along its inferior border, which is directed inward. 
As preserved, the groove is not more than 13 inch long, hence 
the symphysis could not have occupied more than an inch in front 
of the groove. 
Externally the specimen consists of an inferior part, convex from 
above downward, corresponding to the internal groove, and there- 
fore extending longitudinally from behind forward, bulging out so as 
to widen the jaw to 3 inch, and dying away in front, where the jaw 
is moderately convex from the alveolar margin downward. Above 
this longitudinal inferior convexity the bone is very slightly chan- 
nelled in length, being slightly concave from above downward. 
Along this space are several vascular perforations at irregular 
distances, which become small and more numerous towards the an- 
terior extremity of the specimen. The extreme depth of the frag- 
ment as preserved, at the posterior fracture (Pl. XXXYV. fig. 1 a), is 
about 14 inch. 
This form of jaw has hitherto been described in no British Dino- 
saur; but on some future occasion I expect to be able to show that 
an animal with a similar mandible has left its remains in the 
Gosau beds of Austria, which are also of Upper Greensand age. 
Tur VERTEBRAL CoLumN. 
Cervical Vertebre.—None of these vertebre have the neural arches 
preserved, and all have the margins of the centrums and the tu- 
bercle for the rib worn. This gives rise to some uncertainty as to 
whether the sixth vertebra is not rather a first dorsal, as I incline 
to believe. The five vertebra (Plate XXXIV. fig. 1) are similar 
in size, and measure 77 inches in length when placed in close suc- 
cession, without making any allowance for the intervertebral carti- 
lages. The earliest vertebra preserved has the centrum somewhat 
depressed ; but the centrums increase slightly in depth as they 
succeed each other backward, and decrease slightly-in length. The 
first (fig. 1, 1), as preserved, is fully 1} inch long, with the anterior 
articular surface worn, so that neither its width nor depth can be 
given with certainty ; though, as widened by the diapophysis, it is 
obviously wider and does not appear to be so deep as the posterior 
articular end. The diapophysis is large, and placed low on the side 
