AMERICAN JURASSIC PLESIOSAURS 345 
adherent to the visceral face of the interclavicle; in some cases probably they 
are wanting entirely. Coracoids not greatly produced outward and backward 
into postero-lateral processes. Fore limb a little larger than the hind limb, 
to which it is very similar in form, the humerus not being greatly expanded at 
its distal and even in the adult. 
The coracoids, shown in Fig. 3a, are strikingly short, and although 
the posterior border is missing, they are so thin at this point that 
nearly the entire bone is probably represented. The anterior 
border is considerably thickened and in the median line extends 
forward in a short, obtuse angle which apparently did not articulate 
with the scapulae. In general form they resemble M. durobrivensis 
Lydekker. They have a width of 310 mm. and are 260 mm. along 
their greatest length. 
The pelvic girdle is represented by a part of the left pubic bone 
from the acetabulum to the median line, the lateral end of the 
right pubis, and the acetabular extremities of the ischia. From 
these the details of the girdle cannot be obtained, but the parts 
present resemble closely those of the above-mentioned species. 
The ventral ribs (Figs. 36, 3c, and 3d) are peculiar on account of 
their massiveness: they greatly exceed those of all other known 
American forms in size, so far as I can learn, and in that respect 
resemble those of the English forms Muraenosaurus, Cryptocleidus 
Seeley, and allied genera. The median ribs are not uniform in shape 
or size, those present ranging from 18 mm. to 30 mm. in thickness 
and from 30 mm. to 37 mm. in width. Some of them reach a 
length of at least 560 mm. ‘The extremities are flattened for a 
considerable distance along the ventral surface for the articulation 
of a row of smaller lateral ones. The number and arrangement of 
these ventral ribs cannot be determined, but it was probably much 
the same as that in Cryptocleidus and Muraenosaurus, viz., a median 
and three overlapping lateral rows. 
The vertebrae are somewhat crushed and badly weathered and 
cannot be described with a great deal of accuracy. There are 
thirteen dorsal vertebrae present, all of which have the spines miss- 
ing as well as most of the arches. The centra are moderately 
biconcave. They are somewhat flattened on the ventral surface, 
the lateral surface, however, being rather deeply concave antero- 
