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MARSUPITES, 
their marginal edge : these form the margin of the 
pelvis, properly so called. 
These sixteen plates are succeeded by 
5. Five semilunar ossicula (^clavicles') , attached 
to the articulating depressions of the scapular 
plates. 
6. Five cuneiform ossicula (cuneiform or hume- 
ral hones)y attached to the clavicles. These are 
the first bones of the arm, and their superior edge 
is divided into two articulations, from which the 
tentacula are sent off. 
7- Numerous reniform ossicula, by which the 
aperture of the pelvis is closed. 
The plates of the pelvis are convex, sometimes 
umbonated in the centre, and ornamented with 
radiated ridges on the external surface. Their 
markings vary in different examples, and even in 
the same individual ; specimens occurring in which 
some of the plates are nearly smooth, and others 
richly ornamented. 
In every instance, however, the edges of the 
plates are more or less crenulated, and when united 
form a suture in the same manner as the scales of 
the tortoise, but they readily separate when the 
chalk is removed. The central or abdominal plate 
is larger, and more dej)ressed, than the surround- 
ing costals ; the latter are readily distinguished by 
their jientagonaly and the intercostals by their he.va- 
f>;onal form. The scapulce are generally less orna- 
mented than the rest of the series, and are easily 
identified by the semilunar cavity in their u})per 
edge ; this articulating surfiice is traversed by a 
longitudinal ridge, with a minute depression in the 
