118 BRITISH SPONQIAD^l. 



skeleton tissues in a section of the sponge taken cor- 

 rectly at right angles to its surface and mounted in 

 Canada balsam to present the appearance of a beauti- 

 fully regular unispiculous quadrangular network. 



" The dermal membrane is translucent, and in the 

 areas of the terminations of the skeleton structures 

 there were a few pores in an open condition. One 

 form and size only of spicula occurs in this sponge, the 

 purely acerate one." 



6. ISODICTYA ROSEA, Bow. s ii, 282 ; in, PL XLIX, figs. 

 1214. 



7. ISODICTYA PYGH^EA, Bow., ii, 313 ; in, PI. LVI, figs. 

 610. 



1861 Haliclona pygmcea, Bowerbank. List Brit. Marine 

 Invert. Fauna (Brit. Assoc.), p. 71. 



Habitat. Sides of rock-pools between tide-marks to 

 the south of Seaham Harbour, Co. Durham. The 

 specimens in all respects closely agreeing with those 

 which occur at Scarborough. The species, as far as is 

 yet known, is confined to the East Coast of England 



CUT.). 



8. ISODICTYA OBSCUEA, Boio. t in, 224 and 303, PI. 

 LXXVT, figs. 1, 2; PL LXXXVII, fig. 11. 



9. ISODICTYA INDEFINITA, Bow., n, 286; in, PI. XLIX, 

 figs. 1517. 



