282 THE MEDALS OF CREATION. Cuap. VIII. ~ 
because the receptacle and arms of some kinds resemble 
when in repose a closed lily or tulip,—are well exemplified — 
in the recent Pentacrinus ; the only known living form ~ 
that is identical in structure with the numerous extinct — 
tribes, that swarmed in the seas of the palzeozoic and 
secondary ages. | : 
The Pentacrinus (P. caput-meduse, Wond. p. 647), is an — 
inhabitant of the Caribbean Sea, and but rarely obtained ; 
there are specimens in the British Museum* and in the 
Hunterian Collection of the College of Surgeons. 
This animal has a long stem or column, which is com- 
posed of pentagonal calcareous plates or ossicula, articulated 
to each other by radiated surfaces, and is fixed by the base 
to a rock, or other firm body. The column supports a 
vasiform receptacle or cup, formed of calcareous plates in 
close apposition ; in which the digestive and other viscera — 
are situated. The upper part of the receptacle is covered — 
by an integument in which there is an aperture for the 
mouth. From the margin or brim proceed ten multi- 
radiate arms, which subdivide into branches of extreme 
tenuity. On the upper and inner side of the arms are 
numerous articulated feelers or pinne. The ova are situ- 
ated externally on and near the base of the arms, as in the 
Comatulidz ; a family of living Star-fishes, or more properly — 
Crinoids, which have a receptacle, surrounded by articulated — 
and multi-radiate arms, but are free animals, being destitute — 
of a column. 
In the living state of Pentacrinus, the skeleton—for such — 
are the specimens in our museums—was of course covered 
and concealed by the soft integuments and tissues by which 
it was secreted. The ossicula composing the stem are pent- 
angular, and very numerous; they have a central per- 
foration, and their articulating surfaces are ornamented by 
* Petrifactions, p. 77. 
