366 



finding minute spicules in its substance, he placed in his genus Hymeniaci- 

 don, under the name of H. Dujardinii. This genus is of simple character, 

 consisting of membranes with spicules thrown upon them without any kind 

 of defined arrangement. But, here, it is necessary to observe, that in all 

 cases the external membrane, which encloses the sponge, must be well 

 examined. This often differs very materially from the general skeleton, 

 as shown by a section taken at right angles to the surface, which should 

 always be done. For the membrane may have a defined reticulation and 

 other characteristics diverse from the skeleton, and by this you distinguish 

 species, as well as proclaim the alliance between genera. Spicules also 

 may be found of a different form and character in membranes and sarcode, 

 which do not belong to the skeleton. Theacerate spicule, sharp at both ends, 

 and the acuate spicule, as a needle sharp only at one end, form the great 

 staple of the spicules of the skeleton, mostly found in their various modifica- 

 tions of spinous, fusiform, pin-like, clavate, &c, whereas the flesh spicule, 

 or that of membranes, takes the anchorate, in its various forms, the stellate, 

 tricurvate, bihamate and forcipiform, &c. 



Although Hymeniacidon may be represented in a very simple condition, 

 yet in a complex multiplication of membranes and spicules it may become 

 a compact mass, as firm as a piece of cork when dry, and thus it is, one of 

 its species is called " Suberea," and foreign observers have even constituted 

 a special genus under the title of " Suberites." 



In the group now selected, the next allied in organization, but 

 separated from Hymeniacidon under the name of Haphiodesma (from the 

 Greek, needle and bond) differs from the former, mainly, that it has 

 fasciculi of spicules, not combined together in a network, but lying indis- 

 criminately and without much order. It seems, nevertheless, to be a 

 definite advance. The genus is exceedingly interesting and worthy of 

 study, and most of its species develope on its membranes beautifully-formed 

 rosettes of anchorate spicules. It also appears to lead up to another genus, 

 where the fasciculi have become a close and compact network, well bound 

 in keratose membrane. This is Desviacidon, a name in its Greek elements, 

 differing little from the predecessor. And, indeed, the close alliance of the 

 two genera may be seen by a classification of the special forms of spicules 

 used, which fact I have noted in my paper on a new species of Raphio- 

 desma.* One of the rarest and most beautiful of this genus is Desmacidon 

 Rotalis (Vide Brit. Spongiadae, Vol. iii). These three genera therefore 

 make a natural group. 



The next group takes us back again to the membrane, and the three 

 genera comprised in it, are not the least interesting amongst British 

 sponges. The first of these is called " Hyin&raphia" another combination 

 of terms previously used. It consists of a simple membrane and spicules 

 lying upon it, not generally with much order, though occasionally in fasci- 

 culi, projecting through the dermal surface. But this extremely simple 

 form of sponge commends itself by a variety of forms of spicules, not seen 



f " Journal Q.M.C." Vol. vi., p. 97. 



