HYMEDBSMIA. 61 



internal defence, attenuato-acuate in form, but very 

 much longer ; a fully developed one measured -jyt incli, 

 and in place of being entirely spined they are only 

 spinous basallyfor about one third of their length, and 

 their mode of disposition is parallel to the plane of the 

 basal membrane, instead of at right angles to it. 

 Their mode of disposition is also very irregular. 

 There are rarely more than two or three fasciculated 

 together, and by far the greater number are singly 

 scattered amidst the interstitial tissues. 



" The three forms of spicula described are the only 

 ones that I could detect in this sponge. The nearest 

 ally to this species in general form and habitat ap- 

 pears to be Hymedesmia pulchella, from which it is 

 readily distinguished by the diflference in. the form of 

 its skeleton and retentive spicula, and especially by 

 the latter ; but the discrimination of the two species 

 requires close examination, as the retentive spicula 

 of the species in course of description do not exceed 

 YToo ^^ch in length, and they are also exceedingly 

 slender in their proportions." 



7. Hymedesmia pulchella, Boiu., n. sp., iv, PI. II, figs. 

 5—8. 



" Sponge coating very thin and delicate. Surface 

 minutely hispid. Oscula simple, dispersed. Pores 

 inconspicuous. Dermal membrane pellucid ; tension 

 spicula long and very slender, acuate; retentive spicula 

 angulated, bidentate, equi-anchorate, minute, propor- 

 tionally rather stout, very numerous. Skeleton- 

 fasciculi loosely and irregularly formed ; spicula long 



