CHAP, IV. ] THE CRUISES OF THE ‘ PORCUPINE, 167 
Operculine of tropical seas, and Biloculinew and 
Triloculine far exceeding in dimensions the littoral 
forms of British shores; and with these were asso- 
ciated Cristellarie of no less remarkable size, pre- 
senting every gradation from an almost rectilineal 
to the nautiloid form, and having the animal body in 
so perfect a state as to enable it to be completely 
isolated by the solution of the shell in dilute acid.” 
Sponges were extremely abundant, but they were 
restricted to only a small number of species; all of 
them with one form or another of the curious an- 
choring habit. Among the Hexactinellide Holtenia 
was the most striking and the most abundant form. 
Hyalonema was also common; but we got few per- 
fect specimens with the sponge and glass-rope in 
connection. ‘The conical sponge heads were very 
numerous; they seemed to have been torn off by 
the edge of the dredge, the rope remaining in 
the mud, and the ropes were frequently brought 
up without the sponge. Almost all the ropes were 
encrusted with the constant ‘commensal’ of Hya- 
lonema, Palythoa fatua. Very young examples of 
Hyalonema, with the whisp from 5 mm. to 20 mi. 
long, had usually no Pylathoa on them; but when 
they had attained above the latter dimensions in 
almost every case one could see the first polyp of 
the Palythoa making its appearance as a_ small 
bud, and its pink-encrusting ccenosarc spreading 
round it. By far the most common sponge in the 
chalk-mud is the pretty little hemispherical corti- 
eate form Tisiphonia agariciformis. This~ species, 
though differing from it greatly in appearance and 
habit, seems to be closely ailied to a strong, heavy 
