430 Mr. C. W. Andrews on the Pectoral and 
With regard to the species there is some difficulty. Mr. Ly- 
dekker has included under Cimoliosaurus plicatus Phillips’s 
species Plestosaurus plicatus, P. hexagonalis, and P. infra- 
planus, as well as Professor Seeley’s Murenosaurus Leedst. 
For the specimen (Leeds Coll. 28), the limb-girdles of which 
are figured in the present paper, he has suggested the specific 
name Cimoliosaurus durobrivensis, considering it separable 
from C. plicatus on account of its somewhat shorter cervical 
vertebrae. Comparison of some six or seven more or less com- 
plete sets of cervical vertebra (including those of the type 
specimens of Murcnosaurus Leedsi and Cimoliosaurus duro- 
brivensis) with one another shows that, apart from variations 
in size and in the extent to which the arches and ribs have 
fused with the centra, no important differences are to be 
found. The size and condition of ossification are probably 
dependent merely on the age and sex of the individual. It 
is, however, possible that the comparatively small individuals 
in which fusion between the arches and centra has already 
occurred may be specifically distinct, in which case the name 
Murenosaurus Leedsi must be applied to them, the type 
specimen of that species being of this form. On the other 
hand, as already remarked, these differences may be merely 
sexual, and, as Mr. Boulenger has shown in the case of the 
Chelonia *, the fusion of other elements with the vertebral 
centra takes place very irregularly, and consequently is of 
little systematic value. For the present, therefore, it seems 
best to regard all the specimens possessing cervical vertebre 
of the type of Plestosaurus plicatus as belonging to that 
species, 
In the present note specimens of the pectoral and pelvic 
girdles which have lately been mounted for exhibition at 
the Natural History Museum are described. These belong 
to the same individual (R. 2428, Leeds Coll. 28), which is 
that for which Mr. Lydekker proposed the name Cimolio- 
saurus durobrivensis. 
The Pectoral Girdle. (Fig. 1.) 
In general form the scapula (sc) resembles that of Orypto- 
clidus, but differs from it in several points, e. g. (1) the posterior 
border of the dorsal ramus near its upper end bears a sharp 
crest, apparently for the insertion of muscle; (2) the dorsal 
ramus widens out much more rapidly towards its base and its 
anterior edge is thin and sharp; (8) the ventral ramus is 
considerably wider, and also has a comparatively thin anterior 
* Trans. Zool. Soc. vol. xiii. pt. 8, p. 309. 
