[ 93 ] 
There are many more Brittle Stars on the local coral 
reefs than Starfishes^ but unfortunately the majority are most 
difficult to preserve, the arms being so long and exceedingly 
brittle. Most fragile are the various species of Ophioihrix, the 
arms of which are beset with dense rows of spines. A spine- 
less, smooth species Ophiolepts anmdosa. It is grey in colour 
with a black star on its disk and black bands across its arms. 
Trkhastcr sp. has long and stout arms the ends of which are 
branched In Astrophyton the arms begin to divide from near 
their base, the branching being repeated many times, the final 
twigs being exceedingly slender, the whole resembling the most 
delicate lace-work. The specimen exhibited was dredged off 
St- John's Island in December 1896, in a depth of 20 fathoms. 
SEA-URCHINS (Echimidea) . 
The Sea-Urchins have lost all traces of arms. The 
majority are more or less sphericat in shape and show a 
five-rayed symmetry- Others are heart-shaped or disk-shaped 
and are bilaterally symmetrical. Imbedded into the skin of a 
typical Sea Urchin we find 20 rows of plates which are;arranged 
like the meridians of a globe and form a continuous shell The 
plates are covered with spines. The lube feet are even more 
developed than in Starfishes. They are arranged over five 
double rows of those plates which are perforated for their 
passage and are called ambulacral plates. The other five 
double rows of plates which lie between the ambulacra! plates 
and are not perforated, are called interambulacral. AH those 
plates and pores are arranged meridionally, from the mouth on 
the lower surface to the vent on the upper surface of a 
Sea-Urchin, as can be seen on any specimen from which the spines 
have been removed. The mouth is surrounded by five teeth 
which internaily are supported by a curious structure of ossicles 
which was first described by Aristotle and who compared it to 
a lantern in shape. This structure has ever since been called 
** Aristotle's lantern". It is seen in any ordinary Sea-Urchin 
which has been cut open. 
Sea-Urchins are divided into three orders, the Regular 
Urchins iRegulurm), the Cake Urchins {Clypeasir&idea) and the 
Heart Urchins iSpaiangoidea). 
The most common of local Regular Urchins is a species 
of Salmacis, It is found on sandy places, is of greenish colour 
and has thin and short spines. Common also, but only on 
coral reefs, is Diadema setasum. It is of dark purple colour and 
