— 317 — 
parated at the juncture (PI. Il., fig. 2, and Pl.,IV., fig. 10, sat and sa2), 
Seeley (1902, p. 599) erroneously reckoned four sacrals in Stereoster- 
num, his mistake being the inclusion of the last two thoraco-luin- 
bars. 
Caudal region. 
The exact number of caudal vertebrae cannot be determided in 
the present material, but there are in all probability sixty or more, 
as in Stereosternum. Those near the sacrum bear heavy ribs, anchy- 
losed with the centra and curving slightly backward near the extre- 
mity. The width of some ofthese from tip to tip is 40 mm. Beyond 
about the seventh or eighth caudal the ribs rapidly dwindle away and 
they are lacking throughout the greater part of the length of the tail. 
At the same time the neural spines increase in length, and be- 
come slender and very oblique in position. The first pair of chevrons 
are borne on the fifth post-sacral. Asin Stereosternum, the mid-cau- 
dals show a distinct «breaking point», and in general the tail region 
of the two genera is quite similar. 
Shoulder girdle. 
Up to the present time the Mesosaurian shoulder-girdle has been 
known only in part, and the figures of the seapulo-coracoid published 
by Gervais (1869), Seely (1892), and Broom (1904) do not agree entirely. 
In the immature Stereosternum figured by Osborn (1903, p. 485) an 
elongate inter-clavicle was present, and Oshborn’s doubtful identification 
of aclavicle is proven to be correct by astudy of the present mate- 
rial, which, fortunately, yields pratically complete information regar- 
ding both chondrogenous and dermogenous portions of the shoulder- 
girdle. The skeleton figured in Plate Ill, presents a ventral view with 
the elements pratically in situ, while figures 10 and 4 show respec- 
tively the outer and inner surfaces of the scapulo-coracoid. Scapula 
and coracoid are completely anchylosed in the adult. The coracoid is 
of oval form, rather square, and slightly notched posteriorly. The 
glenoid fossa is pratically entirely in the coracoid, and is very shallow. 
Immediately anterior to the glenoid fossa, at the posterior end of the 
lineof scapula and coracoid, is a prominent boss on the outer surface 
and some 3or 4 mm from this hoss the coracoid is pierced by a small 
foramen. There is no evidence of a separate precoracoid, not even a 
