128 A MONOGRAPH OF THE 



acerate spicula are also irregularly distributed. They vary 

 considerably in length and diameter, but they all agree in 

 the abrupt character of the middle curve. 



The skeleton spicula are large, long, and usually per- 

 fectly smooth ; occasionally, but rarely, an incipient spine 

 may be detected at the base with a power of about 300 

 linear, but their occurrence is the exception rather than the 

 rale. 



The internal defensive spicula are short and rather 

 slender. The spines are sometimes strongly developed at 

 the base, but they always present an incipient appearance 

 on the remaining portion of the spiculum. They are 

 seated generally on the basal membrane, but a few are 

 projected from the lower parts of the skeleton columns. 

 In all parts of the interstitial fissures of the sponge the 

 tricurvo-acerate tension spicula are dispersed abundantly. 



I have designated this species I avis, in reference to the 

 rather unusual smoothness of the skeleton spicula. 



3. Microciona fallax, Bowerbank. 



Sponge. Coating, surface rough and uneven. Oscula 

 simple, minute, dispersed. Pores inconspicuous. 

 Dermal membrane pellucid, spiculous ; spicula acuate, 

 long, and slender, dispersed, very abundant. Ske- 

 leton : columns long, slender, and flexuous, occa- 

 sionally branching ; spicula acuate, basally spined ; 

 spines few and minute. Internal defensive spicula 

 attenuato- acute, entirely spined, variable in size, and 

 occasionally very long ; . spines very minute. Inter- 

 stitial membranes, tension spicula same as those of 

 the dermal membrane, comparatively few in number. 



Colour. Alive, bright crimson ; dried, light brown, 

 with a tint of reel. 



Habitat. Diamond Ground, Hastings. 

 Examined. In the dried state. 



I received three specimens of this species from Mr. 



