BRITISH SPONGIAD^. 353 



mass ; the largest is about three inches long by one and 

 half inch wide. The surface in the dry state is exceedingly 

 rugged, irregular, and cavernous, and the oscula are nu- 

 merous, large, and irregular in form. The dermal mem- 

 brane is somewhat thick and opaque, and it is only after 

 having been mounted in Canada balsam that the whole of 

 the spicula with which it is amply furnished can be dis- 

 tinctly seen. The acuate or sub-clavate spicula agree in 

 their proportions in all parts of the sponge, so also do the 

 bihamate ones ; the latter are exceedingly numerous, and, 

 comparatively speaking, are very large (^jBth inch in length) ; 

 they are dispersed on the membranes without any approxi- 

 mation to a regular arrangement. The tension spicula are 

 very numerous, and in the mode of their disposition they 

 often very closely resemble the similar organs in a Hyme- 

 niacidon, so that they appear to form; as it were, a second- 

 ary skeleton very closely resembling that of a species of 

 that genus. 



The habit of this sponge is frequently very like that of 

 Isodictya fucorum, especially on our southern coast, where 

 it is often found enveloping the branches of MhytiphlcBa 

 pinastroides ; but the colour and texture of the two species 

 will readily distinguish them. 



A specimen sent to me by the Rev. A. M. Norman has 

 assumed the coating form. It is an irregular patch of 

 sponge, about four inches in diameter, and very little more 

 than half an inch in thickness, and is of the usual cream 

 colour when in the dried state. It was found at Guernsey. 

 A fragment of another specimen, three quarters of an inch 

 in length, and five lines in thickness, from the same gentle- 

 man, was of a dark brick-red colour. It is very full of 

 sarcode, and has probably its natural colour remaining. In 

 a thin slice from this specimen I found what has every 

 appearance of being one of its gemmules. It was mem- 

 branous, aspiculous, and spherical, and measured g^rd inch in 

 diameter. It was deeply imbedded in the sarcode, and it 

 was the only one I found ; I have thought it better not to 

 include a description of it in the specific character. 



A specimen found encrusting a small boiilder of granite 



33 



