21 
ten rings. Iapprehend that a portion of animal matter remains always be« 
tween the newly-formed ring and the former, perhaps interlacing with the radiat- 
ing muscle where it divides. A proof of this appears to be, that whea decom- 
position affects specimens, and converts them into a sort of ochre, the rings 
will separate, which could not happen, did not animal matterreimain interposed 
from their original formation. 
The enlarged columnar joints (Px. 1v. fig. 8 to 12) are considerably thicker 
than the others, are concave below, and at their superior surface more or less 
convex, with a depression in the centre. They become gradually thinner to- 
wards the middle, and show more numerous and more delicate radiating stria, 
their points of division and the elevated rings are very distinct; at the latter, 
sometimes a series of minute tubercles occur, where probably 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 
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 and 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.1. fig. 2). 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 
PeENTACRINUS 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 pepicue or BASE. (PL, II. 
fig. 1.to 10). I have been fortunate enough to acquire a series of specimens 
