BRITISH SPONGIADiE. 185 



might have been expected, from comparison with the size of 

 the oscnla and pores. 



The crustnlar characters of the dermis of the species under 

 consideration and of H. crustula might, on a superficial exa- 

 mination, lead to their being mistaken for each other ; but 

 in H. p achy derma the crustular dermis is comparatively thin, 

 and the skeleton spicula are not more than two fifths the 

 length of those of H. crustula. 



23. Hymeniacidon crustula, Bowerbank. 



Sponge. Massive, sessile. Surface minutely hispid ; cor- 

 rugated, occasionally mammillated. Oscnla, terminal 

 on the mammillae, or dispersed. Pores inconspicuous. 

 Dermis crustular, abundantly spiculous ; spicula same 

 as those of the skeleton. Dermal membrane pellucid, 

 aspiculous. Skeleton, abundantly spiculous ; spicula 

 fusiformi-aeuate, large, and long. Tension spicula 

 fiisiformi-acuate, slender; occasionally sub-spinulate. 

 External defensive spicula sub-fnsiformi-acuate, short 

 and slender. 



Colour. Alive, buff-yellow or orange-yellow. 



Habitat. Scarborough, Mr. Bean; Guernsey, Rev. A. 

 M. Norman; Diamond Ground, Hastings, J. S. Bower- 

 bank. 



Examined. In the living state. 



I am indebted to my indefatigable friend Mr. Bean for 

 my first knowledge of this sponge. It was found on the 

 beach at Scarborough, at the latter end of March, 1854. 

 The specimen is irregularly cylindrical in form, with hemi- 

 spherical ends 10 lines in length and 6 lines in thickness, at 

 its greatest diameter. Neither pores nor oscula were visible, 

 and the surface was smooth, the dermal membrane having 

 been destroyed apparently by maceration. 



