130 BEITISH SPONGIAD^. 



surface of a fragment of the under valve of a Peden 

 varms about two inclies in diameter, and in no part 

 does it assume a greater thickness than about a line. 

 Its anatomical structure is exceedingly simple and 

 in its present state very fragile. The specimen was 

 probably dead when taken, as both the dermal mem- 

 brane and the sarcodous matter are in a somewhat 

 delapidated condition. What remains of the dermal 

 membrane is very thin and pellucid ; it is very sparingly 

 furnished with very slender acerate spicula, which are 

 nearly equal to those of the skeleton in length, but are 

 rarely more than about one-fourth of their diameter. 

 The skeleton rete is somewhat irregular but decidedly 

 Isodictyal in character : the primary lines are rarely 

 more than unispiculous, but occasionally for short 

 distances they contain two or even three spicula. The 

 secondary lines appear never to be more than uni- 

 spiculous. The spicula are comparatively rather stout 

 and long. 



" The nearest ally to this species is Isodictya Bower- 

 banki. Although in their mode of structure they are 

 very similar, the proportions of their skeleton spicula 

 vary to so great an extent as to at once separate them 

 as species. 



" The spicula of the species under consideration 

 measure xJg inch in length, while those of I. Bowerhanld 

 are -^^ inch in length, and although so much shorter 

 their diameter is greater than those of /. paupercula.'^ 



34. Isodictya olava, Boiv., ii, 316; iii, PL LIII, figs. 

 7—11. 



Habitat. — Dredged off Saints Bay, Gruernsey (N.). 



