160 BBITISH SPONGIAD^. 



both in size and form, but tbe skeleton structure of I. 

 rugosa is very muoh more regular in its arrangement, 

 and tlie strikingly fasciculated arrangement of the 

 spicula of its dermal membrane combined with absence 

 of the small attenuato-acerate spicula that are so 

 abundant in I. inmqualis readily distinguishes the two 

 species." 



70. ISODICTTA DEFOEMIS, Bow., n. sp., IV, PI. XIV, figS. 



1—5. 



" Sponge massive, sessile. Surface irregular, very 

 rugged. Oscula simple, dispersed. Pores incon- 

 spicuous. Dermal membrane spiculous ; spicula dis- 

 persed, sparingly and rather equably acuate or sub- 

 cylindrical, basally incipiently spinous, about the same 

 length, but rather less in diameter than those of the 

 skeleton ; retentive spicula bihamate, small and slender, 

 few in number, and vei-y rarely bidentate-equi-ancho- 

 rate. Skeleton — ^primary lines multispiculous ; se- 

 condary lines variable in the number of their spicula, 

 irregularly disposed acuate, basally spinous, rather 

 short and stout. 



'* Golowr. — In the dried state light brown. 



" Habitat. — ^Wick, North Britain, in deep water ; Mr, 

 0. W. Peach. 



" Examined. — In the dried state. 



" I received a single specimen of this sponge from my 

 friend Mr. C. W. Peach in 1866 too late for publi- 

 cation in vol. ii of this work. It fills nearly the whole 

 of the inner surface of a valve of a common Mussel 

 shell and is neither attractive nor interesting, but on 



