356 ADDITIONS. 



Surface rugose, hispid. Oscula and pores incon- 

 spicuous. Dermal membrane thin, transparent, 

 furnished with a few dispersed bidentate inequi- 

 anchorate retentive spicula. Skeleton. — Primary and 

 secondary lines nearly equally spiculous, disposition 

 of the skeleton irrco-ular and more or less con- 

 fused, lines usually bi- or trispiculous. Spicula atten- 

 uate -acuate, semi-spined basally, rather stout. Internal 

 defensive spicula attenuato-acuate, entirely spined, few 

 in number. Interstitial membranes. Tension spicula 

 cylindrical, slender, and fiexuous ; retentive spicula 

 bidentate inequi-anchoi'ate, minute, dispersed, and 

 simple and contort bi-pocillated anchorate spicula, 

 minute, dispersed. Sarcode abundant, dense and 

 purple in the dried state. 



Colour. — Ahve, light yellow ; Rev. Walter Gregor ; 

 purple ; J. S. Bowerbank. In spiints, dark purple ; 

 when dried, brown with a tinge of purple. 



Habitat. — Strangford Lough ; Messrs. G. C. Hynd- 

 man and Wm. Thompson. Moray Firth ; Rev. W. 

 Greo-or. Hastino-s ; J. S. Bowerbank. 



Examined. — From spirit, alive and dry. 



This sponge is usually found on shells of Pecten 

 opercularis, but I have once found it parasitical on a 

 slender branching zoophyte which it closely embraced 

 in a thin leaf-like form, about two inches in height. 



ISODICTYA INDISTINCTA, Plate LII. 



In examining a series of duplicate specimens of 

 Halichondria ineriistani<, I found among them a 

 specimen so different in its external characters as to 

 induce me to make a microscopical examination of it, 

 and it proved to be the largest specimen of Isodictija 

 indistincta, I had yet seen. It is a widely conical- 

 formed mass, the apex of the cone being the base of the 

 sponge. It is firuily attached to a small fragment of a 

 bivalve shell, about an incli in breadth, and from this 



