ISODICTTA. 157 



for either of the very few British, species to which it 

 is anatomically allied, but from the peculiarities of its 

 structural characters it requires more than the usual 

 amount of circumspection in its examination to deter- 

 mine its species with certainty." 



69. ISODICTYA IN2EQUALIS, Bow., n. sp., IV, PL XVI, figs. 



16. 



" Sponge massive, sessile, cavernous. Surface very 

 rugged and full of elevated ridges and deep depressions. 

 Oscula simple, dispersed. Pores inconspicuous. 

 Dermal membrane abundantly spiculous ; tension 

 spicula dispersed, subfusiformi-acerate, with obtuse 

 terminations, or cylindrical, long and slender, not very 

 numerous, and attenuato-acerate small and short, very 

 numerous. Retentive spicula, bidentate equi-ancho- 

 rate, few in number ; and bihamate simple and con- 

 tort, small and slender, rather numerous. Skeleton 

 diffusive, irregular ; primary lines multispiculous ; 

 secondary lines irregularly disposed, variable in number 

 of their spicula; spicula subfusiformi-acuate, basally 

 and apically spinous, rarely entirely spinous ; spines 

 few in number. Interstitial membranes tension 

 spicula attenuato-acerate, small and short, numerous ; 

 retentive spicula same as those of the dermis. 



" Colour. Dark brown in the dried state. 



" Habitat. 



" Examined. In the dried state. 



" I received a small specimen of this species from my 

 friend the Rev. A. M. Norman, who obtained it among 

 others from Mr. D. Robertson. It is a small mass, 



