122 BRITISH SPONGIADii!. 



20. IsODiCTTA MaoAjstdeewi, Boiv., II, 284; iii, PI. 

 XLIX, figs. 9—11. 



Habitat. — Abundant on Pecten maximus, Lutraria, 

 and other dead stells dredged in Birterbuy Bay ; also 

 in Roundstone Bay, and Westport, Co. Mayo (N.). 



" Among the numerous specimens of British sponges 

 sent to me for examination by the Rev. A. M. Norman 

 I found among those dredged in Westport and Round- 

 stone Bays more than a dozen specimens of J. MacAn- 

 drewi. The largest of them rather exceeded the 

 size of the type-specimen described in vol. ii, p. 284, 

 'Mon. Brit. Spongiadse.' Their external characters 

 were also in accordance with those of the type- 

 specimen. I did not detect gemmules in any of them, 

 but their anatomical characters were identical with 

 those of the described specimen. Along with them I 

 also found a specimen of Isodictya fistulosa, which 

 in some cases might be readily confounded with 

 J. MacAndrewi. The size of the spicula and their 

 mode of arrangement in the skeleton and dermal mem- 

 brane very closely resembles those of J. MacAndrewi, 

 but they are readily to be distinguished, by close 

 observation, when sections of 'the two species are 

 mounted in Canada balsam, by the aid of a power of 

 about 200 linear, by the numerous external spicula 

 projected from the dei'mal membrane of/. MacAndrewi, 

 and the total absence of those organs on the dermis of 

 I. fistidosa." 



