File:The Quarterly journal of the Geological Society of London (13936901182).jpg

•54 1TR. E. LYDEKKER ON THE REMAINS AND AEEINITIES
form, it remains to consider its generic position. At the time
when I first brought the subject of this part of my paper under the
Society's notice, I was inclined provisionally to employ the term
Plesiosaurus in the wide sense in which it has been used by Mr
Hulke. Subsequent experience has, however, led me to the con-
clusion that it is advisable to separate from that genus not only those
Post-Liassic forms which I have already incidentally mentioned under
the name of Cirnoliosaurus, but also the present species and certain
kindred forms. I shall confine, then, the name Plesiosaurus to
those Sauropterygians having a neck of considerable length, compa-
ratively small heads and teeth, the cervical vertebras more or less
elongated, and usually with double costal facets and firmly anchylosed
arches, and the pectoral girdle with a comparatively large omosternum,
Fig. 9.
Part of pectoral limb of Peloneustes philarchus. (About £.)
fe, humerus

t, radius

/, ulna

t\ radiale

i, intermedium

/', ulna e.
formed of two elements

the scapulae being widely separated in the
ventral middle line, with a small and concave ventral surface, and a
very large dorsal portion extending throughout the length of the bone,
and no median union between their ventral portion and the coracoids.
In those forms which I propose to include in Cimoliosaurus the
neck is usually greatly elongated; the head and teeth are very
small

the cervical vertebras are more or less elongated, with single
costal facets, and often complete anchylosis of the arches and ribs
with the centra

while the pectoral girdle is devoid of an omoster-
num, and has the ventral part of the scapulae very large and flat,
and the dorsal part greatly reduced in size, the ventral plates
meeting in the median line, and sending down a median bar to join
the coracoids, which are produced in the middle in advance of the
glenoid cavity. This genus I regard as a branch in one direction
from Plesiosaurus, while another branch has culminated in Plio-
saurus. In the latter branch I would place the so-called