278 PLATE LXXXIII. 



Habitat. Parasitical on stems of large fuci, Mounts 

 Bay, Cornwall; J. S. Bowerbank. 



Examined. In the dried state. 



The sponge coats, irregularly and thickly, the remains 

 of the stem of a large fucus. It is two and a quarter 

 inches long and one and a quarter broad, and has several 

 branches of Plumularia pennatula growing through its 

 substance. Unfortunately it has suffered so much by 

 maceration that the external characters are very nearly 

 obliterated. The dermal membrane is nearly entirely 

 gone, small portions only remain ; these fragments are 

 sparingly furnished with the smaller description of 

 acuate spicula, with an occasional intermixture of the 

 larger and stouter ones. The position of the oscula 

 are indicated by a few large orifices in the substance of 

 the surface of the sponge. No trace of pores could be 

 detected on any of the fragments of the dermal mem- 

 brane. The external form of the sponge is exceedingly 

 irregular and unprepossessing, but the internal cha- 

 racters are amply sufficient to determine the species. 



The skeleton is remarkable in its structure, the fibre 

 is furnished abundantly with spicula disposed in a 

 central line ; these spicula are small and slender, and 

 are much too numerous and too closely packed together 

 to be counted, and it is only occasionally near the outer 

 portion of the fibre that the large and comparatively 

 long spicula of the skeleton are found disposed singly ; 

 and it is rarely that they are found intermixed with the 

 central line of slender spicula. This mode of structure 

 is very singular, and I do not remember to have observed 

 it before in any species of chalina. It therefore forms 

 a very prominent character in the discrimination of the 

 species. 



The respective differences of the two sizes of spicula 

 in C. inornata as compared with each other may be best 

 expressed by their average measurements. Thus the 

 larger ones were -jnhj inch long and greatest diameter 

 3-^25- inch ; while the smaller ones were -^-^ inch long 

 and their greatest diameter irsVs inch. 



