CHAP. II. ] FROM PORTSMOUTH TO TENERIFFE. 141 
lum is very frequently inhabited by one, sometimes by a pair, 
of a “commensal” decapod crustacean ; indeed, the association 
is so constant that only a few years ago a paper was written to 
show that the sponge was a wonderful siliceous habitation con- 
structed by the crab! It is singular that while Palythoa fatua 
is as constantly associated with examples of //yalonema from 
the coast of Portugal as with those from Japan, no commensal 
crustacean has been found in any of the Atlantic specimens of 
Luplectella. 
We were greatly interested in adding one of these singular 
sponge-forms to the fauna of Europe. uplectella belongs to 
a very special group of sponges which have been called the 
HexactIneLiip&, from the circumstance that the siliceous spic- 
ules throughout the whole family appear to be six-rayed. This 
fundamental form is often curiously masked—one, two, three, 
or four of the rays being frequently suppressed ; but when this 
is the case, some branching or splitting of the central canal, or 
some symmetrical arrangement of projections in the ornament 
of the spicule, is sure not only to refer it to its ground-form, 
but to give some clue to the particular kind of suppression or 
modification which has taken place. 
The HerxactineLiip® are a beautiful family. Besides “w- 
plectella, which is perhaps the flower, it contains //yalonema, 
the glass-rope sponge of the Atlantic and the North Pacific; 
A phrocallistes, another beautiful lacey fabrie of flint ; /Zoltenia, 
Rossella, Poliopogon, and many other wonderful genera. The 
group belongs specially to the fauna of the deep sea, and they 
seem to thrive best among the elements of nascent limestones. 
They are an old family, abounding in many graceful shapes in 
the beds of chalk and greensand of the South of England; but 
until lately the fossil “ ventriculites” were supposed to be ex- 
tinct, and the discovery of their descendants living in the mod- 
ern chalk-beds of the Atlantic was one of the most interesting 
of the many corroborative evidences in favor of the view of 
I.—10 
