HYMEDESMIA. 59 



from three or four to so many as to render it quite 

 impossible to count them. 



" The defensive spioula are very much stouter than 

 those of the skeleton. They are very numerous ; a 

 portion of them are based on the inner surface of the 

 basal membrane, and are projected into the mass of 

 the sponge at various angles, while others are pros- 

 trate on the membrane, or intermixed with the skeleton 

 tissues. 



"The arcuate, bidentate, equi-anchorate, retentive 

 spicula, are exceedingly numerous. They are very 

 slender, and are abundantly but irregularly disposed 

 in every part of the structures. 



" The only species of Hymedesmia with which H, 

 pansa might possibly be confounded is H. indistincta^ 

 which has acuate, skeleton spicula, and bidentate, equi- 

 anchorate, retentive ones, but it has no such internal 

 defensive spicula as those which abound in H. pansa." 



6. Htmbdbsmia hlata. Bow., n. sp., iv, PI. II, figs. 1 — 4. 



" Sponge coating very thinly. Surface smooth or 

 minutely hispid. Oscula simple, dispersed. Pores in- 

 conspicuous. Dermal membrane pellucid, rather abun- 

 dantly supplied with very minute, simple or contort, 

 bihamate, retentive spicula. Skeleton having the fasci- 

 culi rarely containing more than two or three spicula, 

 more frequently singly dispersed; spicula attenuato- 

 acuate, basally spinous, long and rather slender. In- 

 ternal defensive spicula attenuato-acuate, entirely spi- 

 nous, comparatively short and stout, very numerously 

 projected at right angles to the membranes. 



