135 
CRINOIDS, STAR-FISH, SEA-URCHINS, ETC. 
Cases 3 and. 4 and Tal>le Cases* — The class of ani- 
mals designated by the term Echinodermata (having a prickly 
covering) includes the Crinoidea (sea-lilies, etc.), the Ophiuroidea 
(brittle-stars and basket-fishes), the Asteroidea (star-fish), Echi- 
noidea (sea-urchins), and the Holothuroidea (sea cucumbers). 
These are exhibited in the Wall-cases 3 and 4, and in Table-cases 
5 > 7 > 8, 9, 10, II and 12. The series begins with Table-case 5. 
The class takes its name from one of the most obvious char- 
acteristics of the group— the possession of a covering of spines- 
These spines undergo the most extraordinary modifications, not 
only in the different groups of the class, but even in different 
parts of the body of some individuals. They are sometimes 
wholly wanting. 
Case 5. — Here are shown the lowest forms of the class, the 
Crinoidea, Many species are furnished with a long stem, by 
means of which the animal is attached to some fixed object. 
Comparatively few species now exist, but in some of the earlier 
geological periods the crinoids were extremely abundant. In 
Wall-case 3 are shown some alcoholic preparations. 
In Case 5 are also exhibited the Ophiuroidea, some of which 
are known under the names brittle-stars and serpent stars ; others 
as basket-fishes; although they are in nowise related to true 
fishes. Some of them are remarkable for their very long and 
attenuated arms. The basket-fish (Asirophyion) is remarkable 
for its branching arms. 
Cases 6, 7, 8 and part of 9.— Specimens of the order 
Asteroidea (star fishes). The simplest form of these animals is a 
central disk passing gradually into five arms ; but there are ex- 
treme modifications of this pattern. The arms may be more 
numerous and very long or very short. The five arms may form 
simply the angles of a pentagon, or they may form the greater 
portion of the animal. Some of the larger species are exhibited 
in Wall-case 4. 
Cases 9, lO, 11 and 12. — In Echinoidea^ 
or sea-urchins. The skeleton of all these consists of ten zones of 
plates closely joined and forming a sort of box. On the outer 
surface of this is an armature of spines. The form of the animal 
