BRITISH SPONGIADiE, 201 



the difficulty, as there is a striking similarity of form be- 

 tween the spicula of the two species under consideration ; 

 but although this close approximation in form exists there 

 is so great a difference in their proportions as to render 

 their ultimate separation distinct and certain ; go much so 

 that an experienced observer may readily determine the 

 species by the spicula alone. The following measurements 

 derived from the spicula of the type specimens of the two 

 species in the Johnstonian collection in the British Museum, 

 will best illustrate their differential characters. One of the 

 largest spicula from H. carnosa measured j^th inch in 

 length, and jsWnd inch in diameter. An average-sized 

 one was ^th inch long, and j^th inch greatest diameter, 

 while in H. suberea, one of the longest spicula I could find 

 measured ^th inch in length, and gn^rd inch in diameter, 

 and an average-sized one ^rd inch long, and jg^th inch 

 greatest diameter. I have examined a considerable number 

 of specimens of each species, and I have found their pro- 

 portional- differences to exist in every case. In both sponges 

 the spicula are subject to malformation and of irregularities 

 in the development of the spinulate bases, and therefore the 

 differences in their proportions become the more valuable 

 as differential characters. 



A favorite locality of H. suberea is on the shells of 

 various species of Turbo, Pusus, and other univalves, which 

 it often entirely envelopes, intruding itself frequently far 

 into the interior of the shell, although it may be also 

 occupied by a Pagurus. In a specimen assuming the form 

 of a compressed Hyvieniacidon ficus, and of about or rather 

 larger than the usual size of f^hat species, partially enveloping 

 a shell of a T'usus, the mollusc was evidently alive at the 

 time of the sponge locating itself, as the whole of the face 

 of the shell, from the apex of the whorls to the extreme 

 point of the canal for the passage of the siphuncle of the 

 mollusc, is perfectly clear of the sponge, while the whole of 

 the back of the shell is as completely covered by it ; but 

 notwithstanding' that it does not at any part pass over the 

 edge of the shell, it has not succeeded in gaining possession 

 of the interior within the last whorl for nearly an inch. 



