130 BEIT1SH SPONGIAD^E. 



surface of a fragment of the under valve of a Pecten 

 varius about two inches in diameter, and in no part 

 does it assume a greater thickness than about a line. 

 Its anatomical structure is exceedingly simple and 

 iu 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 Boiuer- 

 banJci. 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 yjg- inch in length, while those of I. Bowerbanki 

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

 their diameter is greater than those of /. paupercula." 



34. ISODICTYA CLAVA, Bow., n, 316; in, PI. LIU, figs. 

 711. 



Habitat. Dredged off Saints Bay, Guernsey (N.). 



