158 A MONOGRAPH OF THE 



3. Hymeniacidon brettii, Bowerbank. 



Sponge. Encrusting, surface smooth, minutely reticulated. 

 Oscula simple, small, dispersed. Pores inconspicuous, 

 numerous. Dermal membrane rather stout, pellucid, 

 abundantly spiculous. Spicula of the skeleton fusi- 

 formi-acerate, stout ; tension spicula of the interstitial 

 membranes acerate, slender. 



Colour. Alive, externally cream, internally yellow. 

 Habitat. Tenby, Mrs. Brett and J. S. Bowerbank ; 

 Menai Straits, Mr. Alder. 



Examined. In the dried state. 



I received this species, among others, from Mrs. Brett, 

 of Tenby, by whom it was found on St. Katherine's Rock, 

 between high and low water marks. The sponge was 

 nearly covered by a specimen of Isodictya rosea. It is 

 nine lines in length, six in breadth, and does not exceed 

 three in thickness. The surface is undulating and smooth, 

 and is minutely reticulated ; when viewed through an inch 

 lens it has much the same appearance as that of Halichon- 

 dria panicea, but the reticulations are finer than in that 

 species. The oscula are very small, not exceeding one 

 third, or one fourth, of a line in diameter, and although so 

 minute they are not numerous. The pores are abundant 

 and equally distributed over the whole of the surface, and 

 are in a great measure the cause of its reticulated appear- 

 ance. The dermal membrane is rather stout, but pellucid. 

 It is abundantly spiculous, and the spicula are collected 

 into loose, and often continuous fasciculi, which have a 

 tendency to cross each other at nearly right angles ; the 

 prevailing spicula are the slender acerate ones, but there is 

 a considerable intermixture of the stout fusiformi-acerate 

 ones of the skeleton. 



I have named it in honour of its discoverer, Mrs. Brett, 



