120 
ECHINITES. 
able spines ; tlie mouth being placed beneath. 
The crust or covering is composed of an im- 
mense number of plates, varying in form in dif- 
ferent families, and in some species amounting to 
nearly a thousand in one individual. It has nume- 
rous })erforations, tlirougli which tlie tentacula of the 
enclosed animal are protruded. These pores form 
bands (^amhulacrci) that divide the shell into seg- 
ments (arecp')^ the latter being more or less covered 
with tubercles, to which the spines are attached by 
strong ligaments. Upon the death of the animal, 
these ligaments undergo decomposition, and the 
spines almost constantly fall off, — a circumstance 
that explains the cause of their being so seldom 
found in connection with the shell, in a fossil 
state. The mouth is armed with five or six trian- 
gular teeth. 
These animals feed upon crabs and the lesser 
kinds of shell-fish, whidi they seize and convey to 
the mouth by means of the tentacula, the spines 
being the instruments of motion.* 
The remains of the numerous family of echinidae 
occur in the chalk abundantly, and those of the 
genera Galerites, Ananchytes, Spatangns, and Ci- 
daris (the latter more rarely), are among its most 
characteristic productions. Their cavities are com- 
monly filled up witli silex, which presents a j)erfect 
cast of the interior, after the crustaceous covering’ 
has been removed by chemical or meclianical 
agency ; fossils of this kind are very frecpiently 
found among the beds of loose flints on the surface 
* Hecs’s Cydop.Tdia, art. Ech'mm. 
