HTMEDESMIA. 63 



with the equi-anchorate retentive spicula, which are 

 abundantly distributed on the inner surface of the 

 dermal membrane. 



" The skeleton fasciculi are very irregularly con- 

 structed, and they rarely contain more than four or five 

 irregularly placed spicula; but in addition to the fasci- 

 culi there are numerous single spicula dispersed among 

 the fasciculi, and also a considerable number of the 

 long, slender, basally spined, attenuato-acuate spicula, 

 which are mostly prostrate amidst the other portions of 

 the skeleton, though occasionally a few of them have 

 their apical extremities slightly elevated above the sur- 

 face on which their bases repose. These spicula are 

 strikingly distinct from the purely defensive ones of the 

 sponge, from which they may be at once distinguished 

 by their being only basally spinous, and by being 

 about three times the length of the purely defensive 

 ones ; an average-sized one measured y^-Q inch in 

 length ; they are basally spinous for about one fourth 

 of their length ; the spines are acutely conical, but 

 neither strongly nor numerously produced, while the 

 internal defensive ones have their spines abundantly 

 and very strongly produced, and especially so at their 

 bases. The latter forms, besides those projected at 

 rather regular intervals at right angles to the basal 

 membrane, are frequently found prostrate on the mem- 

 brane, either singly or in clusters, and occasionally 

 assume a somewhat fan-shaped mode of disposition. 



" The angulated bidentate, equi-anchorate, retentive 

 spicula are very numerous ; they vary very slightly in 

 size a fully developed one measured yaVf inch in 

 length and are rather stoutly proportioned ; they 

 require a power of about 500 linear to render them 



