0َ 
iil is‏ و 
| 
| 
M 
i 
a | 
| 
| 
j 

II 
21 
rings. 1 apprehend that a portion of animal matter remains always be-‏ ما 
tween the newly-formed ringand the former, perhaps interlacing with the radiat-‏ 
ing muscle where it divides. A proof of this appears to be, that when decom-‏ 
position affects specimens, and converts them into a sort of uchre, the rings‏ 
will separate, w hich could not happen, : did not animal matterremain interposed 
from their original formation. 
The enlarged columnar joints (Pr. 1v. fig. 8 to 12) are considerably thicker 
than the others, are concave below, and at their superior su 
convex, with a depression in the centre. 
wince Ure روز‎ CSN 
They become gradually thinner to- 
wards the middle, and show more numerous and more delicate radiating striz, 
their points of division and the elevated rings are very distinct; at the latter, 
sometimes a series of minute tubercles occur, where — the covering - 
periosteum adhered more firmly. In consequence of the concavity of the inferior 
surface having a greater curvature than the convexity of the superior surface, 
each joint is thinnest towards the centre, and hence a hollow lenticular space 
of a concavo-convex figure is formed between the two contiguous joints, which ۰ 
may be considered as an enlargement of the alimentary canal. The joints 
adhere by the last-formed rings, which probably afford a firmer connexion 
from their being less calcareous, and are kept together more firmly by the thin 
exterior muscle interlacing with the radiating ones. Their circumference ,is 
somewhat less below, and contracts a little at the superior aud lower surfaces. 
Near the point of junction of the enlarged and unenlarged portion of the 
column, an alternation of thicker with thinner joints, may very generally. be 
observed (T. r. fig. 9). “This is common to all the Crinoidea, and has been ex- 
plained as a provision of nature, to allow a greater power of motion to- the 
portion of the column where it approaches to the parts destined to procure the 
animal's food. But I am convinced that this was also the place where new 
/ joints are continually formed, at least as long as the energy of life permitted; 
/ thus increasing the length of the column, as will be proved when describing 
PENTACRINUS CAPUT MEDUSE, 
The column at its lower extremity is more or less surrounded by calca- 
reous matter of laminar construction, thereby adhering to extraneous sub- 
stances; this has been called by Mr. Parkinson the PEDICLE or BASE. (Pr. 11. 
fig. 1. to 10). Ihave been fortunate enough to acquire a series of specimens 
D.‏ وت 
