132 A MONOGRAPH OF THE 



5. Microciona spinulenta, Bowerbank. 



Sponge. Coating thin. Surface rugged and uneven. 

 Oscula simple, minute, numerous. Pores inconspi- 

 cuous. Dermal membrane spiculous ; spicula cylin- 

 drical, sub-clavate, long and slender; dispersed or 

 sub-fasciculate, numerous. Skeleton. Columns short 

 and small ; spicula attenuato-acuate, entirely spined ; 

 spines acutely conical, strong, and numerous. In- 

 ternal defensive spicula same as those of the skeleton, 

 few in number. Tension spicula of interstitial mem- 

 branes same as those of dermal membrane. Retentive 

 spicula bidentate inequi-anchorate and unipocilate 

 and bipocilate bihamate, dispersed, very minute and 

 few in number. 



Colour. Dark brown when dried. 

 Habitat. Squin Ground, Weymouth Bay, J. S. Bower- 

 bank. 



Examined. In the dried state. 



I dredged this species, in 1847, on the Squin Ground, 

 in Weymouth Bay, near the wreck of the Abergavenny. 

 It covers the shells of Peden ojjercularis more or less, but 

 always very thinly. It appears to be very common in 

 that locality. I do not recollect the colour in the living 

 state. In the dried condition it is a dark nut-brown. 

 When examined by direct light with a two-inch combina- 

 tion, the surface presented a very rugged and uneven 

 appearance, but in the living state it would probably be 

 much more smooth and even. The oscula are small and 

 numerous ; the largest of them may be seen by the aid of 

 a lens of two inches focus. 



The dermal membrane is profusely furnished with tension 

 spicula, which are dispersed, or very loosely and irregularly 

 fasciculated. The spicula are slender, long, and usually 



