52 
ROOM X. 
Nat. Hist. 
Egg (. Echinus trigonarius ), and the Artichoke, or 
Black Sea-Egg ( Echinus atratus), peculiar for the 
larger spines being very short and truncated, forming 
a smooth surface, somewhat resembling a tessellated 
pavement. In some species with spines of unequal 
size, the tubercles to which they are attached are 
pierced in the centre ( Cidaris ). Those called Tur¬ 
bans are of a spherical form, and have very narrow 
wavy rows of pores, as the Imperial Turban ( Ci¬ 
daris imperialis) and the Porcupine Turban ( Cidaris 
hystrioo ); while those which are depressed, with narrow 
separate rows of pores, are called Diadems. These 
often have tubular spines, as the common Diadem ( Echi¬ 
nus diadema). 
Several of the species of the orbicular kind live in 
holes in rocks, and are believed, by some authors, to 
have the faculty, like the Piddock (. Pholas ), of boring 
into their substance. 
The Star-Fish (AstericeJ, Nos. 9—16, have the body 
depressed and more or less divided into rays, and the 
stomach furnished with only a single aperture. They 
have been separated into several groups, the first con¬ 
taining those with a small orbicular body and long* 
subcylindrical arms, as the Medusa’s Heads (Eu- 
ryale) , which have the arms very long, with com¬ 
plex ramifications, so as to end in an immense multi¬ 
tude of small threads. In most of the species the arms 
are branched at the base, but in one (Euryale palmi- 
feraJ, the base of the arms is simple, and the tip re¬ 
peatedly ramified. 
The Ophiurae have also very long and slender arms, 
but they are always simple. In many of the species the 
arms are furnished on each side with several series of 
minute, moveable spines. 
The arms of the true Star-Fish (Asterias) are a mere 
extension of the substance of the body, and of an uni¬ 
form structure with it. Most of the species have the 
faculty of reproducing the arms, or such parts of them 
as may be accidentally broken off; and if an entire arm 
be 
