Apr. 1903. NorrH AMERICAN PLESIOSAURS —WILLISTON. AZ 
cation of this cartilage evidently occurs in some forms, uniting the 
whole into a single ventral plate, which is said to have a sutural con- 
nection with the epicoracoid processes, forming what Seeley calls the 
Elasmosaurian type of girdle. Seeley suggests that this cartilage 
may represent the precoracoid: ‘In all Plesiosaurs, on the other 
hand, the precoracoid, if developed, remains cartilaginous; but I 
infer that a cartilage always extended from the anterior margin of the 
coracoid to the anterior extremity of the scapula, and, by ossification 
of such cartilage, the Plesiosaurian shoulder girdle would become 
Elasmosaurian.”’* 3 : 
This precoracoid nature of the cartilage is contested by Koken: 
‘<The view that the bone considered to be the scapula in the Plesio- 
saurs also includes the precoracoid is supported neither by compar- 
ison nor observation. In no reptile has there been shown to bea 
union of the scapula with the precoracoid more intimate than its 
union with the coracoid, and its fusion with the scapula without 
union with the coracoid would be remarkable. I agree quite with 
Baur, who considers the forked bone of the turtles to be the scapula 
only, its two branches being homologous with those of the plesiosau- 
rian scapula. Seeley believes that the precoracoid was cartilaginous, 
connecting the front end of the coracoid with the anterior end of the 
scapula, and that this became ossified in the Elasmosaurians in such 
a way that it was separated from the coracoid by suture, but was 
fused with the scapula. That is, it is the precoracoids and not the 
scapula which meet in the middle line. It seems to me that this 
would be the method of extension and ossification of the scapule. 
Why, then, should we call in the aid of a cartilaginous precoracoid as 
an unknown quantity, which later becomes indistinguishably fused 
with the scapula?”’+ 
The precoracoid arises from a distinct ossificatory center, when 
ossified. Is it reasonable to suppose, then, if this is,a distinct ele- 
ment, that any such mode of extension of the scapula as Andrews has 
shown to be the case in Crvptoclidus oxoniensist would occur if there 
was really a union of scapula and precoracoid? He shows clearly 
that the scapula increases in length peripherally, and not by the addi- 
tion of an ossified cartilage. . If it arose from a distinct center, as it 
must, one would certainly expect to find it in a separated condition 
in the young animal, but this was not the case in the ones that 
Andrews examined. Furthermore, in what possible way could a carti- 
*Proc. Roy. Soc. Lond. li, p. 138, 1892. 
+Koken, Zeitschr. Deutschen Geol. Gesellsch. 1893, xlv, 346. 
tAnn. Mag, Nat. Hist. 1895. 
