ON THE REMAINS AND AFFINITIES OF MESOZOIC REPTILES. 41
2. On ^Remains and Affinities of five Genera of Mesozoic R,ep-
tiles. By R. Lydekker, Esq., B.A., E.G.S. (Head November 21,
188S.)
.Plate II..
Introductory.
The following communication treats of certain remains referred to
four species of English Mesozoic Reptiles, some of which were first
described or named by Professor H. G. Seeley, and also includes
a discussion as to the affinities of a fifth form. The substance of
that portion of the paper relating to Peloneustes pTiilarchus was pre-
viously brought under the notice of the Society at the Meeting held
on May 23rd as a separate communication, entitled " On the Skeleton
of a Sauropterygian from the Oxford Clay near Bedford "

• ,

but, on
account of a change of view on the part of the Author, it was con-
sidered advisable that it should be again presented in a revised
form.
I. Vertebra of an Ornithopobous Dinosaur from the
Cambridge Greensand.
On page 621 of a memoir on the remains of Dinosaurs from the
Cambridge Greensand, published in the 35th volume of the Society's
' Journal,' Professor Seeley applied the name Si/ngonosaurus macro-
cercus to a series of nineteen vertebras from the cervical, dorsal,
sacral, and caudal regions, which were said to be associated, and
indicate a medium-sized species. At the conclusion of the descrip-
tion of these vertebras mention is also made of certain dermal
scutes, which it was suggested might also be associated. I have no
intention of entering into the question whether the alleged associa-
tion of all these remains is absolutely certain, and I shall accord-
ingly confine my remarks to the one cervical and eight dorsal
vertebras, which, as being the first described (although not figured),
may, I presume, be regarded as the types.
All the dorsals are amphiccelous, and characterized by their
compressed centra to which the arches are firmly united, the
absence of rib-facets on the arches, and the height of the neural
canal. In the four anterior dorsals the centrum is comparatively
short, with triangular terminal faces and a sharp hasmal ridge

while in the four later ones the centrum is longer, the haemal ridge
disappears more or less completely, being represented by a tubercle
at either end f , and the terminal faces are less triangular. In the
anterior dorsals the length of the centrum varies from 1*5 to 1*7
inch

while in the first of the four later ones this length is 1*75,
and the height from the base of the centrum to the summit of the
neural platform 2" 5 inches.
Prof. Seeley makes no attempt to determine the serial position of

Proc. Geol. Soc. 1888, p. 89.
t I take the character from page 621 of Prof. Seeley's memoir

there is
some discrepancy with this on p.