:HAP. iv.] THE CRUISES OF THE ' PORCUPINE: 1 (57 



OperculincB of tropical seas, and J3ilocnlinw and 

 Triloculince far exceeding- in dimensions the littoral 

 forms of British shores; and with these were asso- 

 cated Cristellarice of no less remarkable si/e, 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 Ilexactinellidie Ifollcnia 

 was the most striking and the most abundant form. 

 Hyaloncnia 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 

 Ilyaloncma, with the whisp from 5 mm. to 20 mm. 

 long, had usually no Palylhoa 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 

 hud, and its pink-encrusting co^nosarc spreading 

 round it. By far the most common sponge in the 

 chalk-mud is the pretty little hemispherical corti 

 cate form Tisiphonia agaric if or mis. This species, 

 though differing from it greatly in appearance and 

 habit, seems to be closely allied to a strong, heavy 



