A MONOGRAPH OF THE 



22. Hymeniacidon pachyderma, Bowerbanh. 



Sponge. Massive, sessile ; surface corrugated. Oscula 

 small, simple, dispersed. Pores inconspicuous. Der- 

 mis crustular thin, abundantly spiculous; spicula 

 acuate, stout, matted closely together. Dermal mem- 

 brane thin, pellucid, aspiculous. Spicula: of the 

 skeleton, acuate, rather stout and short, occasionally 

 bent near the base ; tension spicula acuate, slender, and 

 often sinuous. 



Colour. — Dried : external, cream colour ; internal, light 

 brown. 



Habitat. — Torquay, Mrs. Griffiths. 

 Examined. — In the dried state. 



I am indebted to my late friend Mrs. Griffiths, of Torquay, 

 for two specimens of this species. Neither of them exceeds 

 an inch in length, by three fourths of an inch in breadth and 

 half an inch in thickness. The surface in each is corru- 

 gated, but much more so in one than in the other ; in the 

 remaining characters they agree very closely. The oscula 

 are small, and require the assistance of a two inch lens to 

 render them distinctly visible, and the pores, even with the 

 aid of an inch lens, are inconspicuous. The crustaceous 

 dermis is about the thickness of a stout sheet of letter paper. 

 It is composed of acuate spicula, like those of the skeleton, 

 closely but irregularly interwoven together, and covered with 

 a thin pellucid dermal membrane, in which no spicula are 

 apparent excepting those belonging to the dermis, to which 

 it adheres closely and firmly. The spicula of the skeleton 

 are rather stout, variable in length, and are frequently more 

 or less bent near the base. The slender acuate tension 

 spicula intermixed with those of the skeleton are frequently 

 much attenuated, and are often sinuous. The interior sub- 

 stance of the sponge is permeated in every direction by 

 canals, which are very much larger and more numerous than 



