CRINOIDEA. 281 
The Echinodermata possess the radiated type of structure 
in an eminent degree ; especially the Asterioide and the 
Kchinide, of which the common Star-fish, and Sea-urchin, 
are familiar examples. The external integument or skin is 
in many kinds protected by spines, (hence the name Echi- 
noderms or spiny-skin,) and perforated by numerous fora- 
mina for the imbibition and transmission of sea-water, and 
for the protection of minute soft tubular processes (called 
pseudopodia), which constitute organs of adhesion and loco- 
motion. 
The first two orders have endo-skeletons, composed of 
numerous ossicula or little calcareous bones: in the third 
order, the KEchinide, the body is inclosed in a calcareous 
ease or shell, formed of numerous plates closely adjusted to 
each other ; in the fourth order, the Sea-slugs, the body has 
only a tough outer integument without movable spines. 
Diversified in form and external appearance as are the 
Invertebrata thus grouped together, they are naturally 
related by their organization. The Crinoidea may be re- 
garded as Star-fishes fixed to one spot by a jointed stem ; 
the Star-fishes as free Crinoidea ; the Echinidze as Star- 
fishes with the rays coalesced and united into a globular 
or spherical case ; and the Holothurie, as elongated Sea- 
urchins, destitute of spines, and without a calcareous 
envelop. 
CrinombEA.—The animals of this order are subdivided 
into families and genera according to the number, form, and 
arrangement of the plates composing the calcareous case or 
receptacle, and the structure of the arms and column. In 
one living family, the Comatulide, the body is free ; and 
in one fossil genus, the Marsupite, the animal is capable of 
locomotion through the water. 
The essential character of the Crinoidea,*—so named 
* From xplvoy, crinon, lily, and ef8os, eidos, a form. 
