168 THE DEPTHS OF THE SEA. [CHAP. IV. 
encrusting sponge which we met with frequently 
sticking to stones in the ‘cold area.’ The form of 
the spicules was nearly though not quite the same, 
and their arrangement was very similar. It appeared 
as if the two forms placed in intermediate cireum- 
stances might have approached one another very 
closely. 
In the warm area, as in the cold at these great 
depths, there is a singular absence of Hydrozoa, A 
few species of Serfularia and Plumularia, and one or 
two allied forms occurred, and they are now in the 
skilful hands of Dr. Allman for determination ; but 
their small number and insignificance is remarkable. 
Neither are the true corals represented by numer- 
ous species, although in some places individuals 
are enormously abundant. During the ‘ Porcupine’ 
cruises of 1869 twelve species of Madreporaria were 
procured which have been determined by Professor 
Martin Duncan. None of these belong to ‘reef- 
building’ genera, but to a group which are recog- 
nized as deep-sea corals, a group which appears to 
have had numerous representatives during all the later 
eeological periods. In a band somewhat restricted 
in depth, extending downwards from the 100-fathom 
line, we met in some places with very large numbers 
of many varieties of Caryophyllia borealis, FLEMING 
(Fig. 4); and at depths of 800 to 600 fathoms the 
handsome branching Lophohelia prolifera, PALAs 
(Fig. 30), forms stony copses covering the bottom 
for many miles, the clefts of its branches affording 
fully appreciated shelter to multitudes of Arca 
nodulosa, Psolus squamatus, Ophiopholis aculeata, 
and other indolent ‘ commensals.’ 
