72 
room x. The mouth is armed with jaws, inserted in five 
triangular spongy bones, and the pores are 
placed in five arched pairs of bands, forming a 
star on the upper part of the shells. 
Some of the species of this group, as the 
Clypeasters , are convex and shield-shaped ; the 
others, as the Scutellce , are very much de¬ 
pressed, and nearly fiat, so that it is difficult to 
conceive how the animal can exist in so thin a 
cavity. Many of the species of this genus are 
pierced with holes through the disk, as the Scu- 
tella quinquifora , Scut, bifora , &c. Others are 
lobed on the margin, as the Eight-rayed Scu- 
tella ( Scut. octodactyla') and Toothed Scutella 
(Scut, dcntata). Others are orbicular, more or 
less depressed, with the two openings of the 
alimentary canal placed opposite each other in 
the axis of the shell, one at the vertex, the 
other at the base, with the series of pores form¬ 
ing bands, and extending from the one to the 
other. These shells are generally covered with 
larger spines and tubercles. 
In many species of this division the spines 
are of nearly equal size, and the tubercles on 
which they are placed are not pitted in the 
centre ( Echinus ); as the common Sea-Egg of 
the English coast ( Echinus esculentus ), which is 
much sought after as food during a part of the 
summer season, at which time the shell is al¬ 
most entirely filled with eggs. Other species, 
in 
