439 



arrival of some other specimen preserved in spirit to determine the 

 fact. At the same time the bark is unlike that of any sponge that 

 I am acquainted with, the existence of such a bark on any true 

 sponge being as yet unknown to me. On the other hand, the ex- 

 istence of an axis of the spongy texture and the silicious composi- 

 tions found in this marine body are novelties in the order of zoophytes 

 in which its general appearance would lead one to place it. But 

 that is no reason why it may not prove to be a zoophyte, as the 

 same may be said to be the case with regard to the genus Hyalonema, 

 the axis of which is so anomalous that several of the French zoolo- 

 gists — Valenciennes, Milne-Edwards, and others — considered the bark 

 of it as a parasite on some unknown substance, overlooking the fact 

 that the bark is strengthened by fibres exactly like those of which 

 the axis is composed. Such an idea would require a belief in the 

 existence of two bodies always found together, and unknown in any 

 other form, instead of their being regarded as parts of the same 

 animal. 



The axis of this body has many characters in common with the 

 body which is called a Sponge described by Mr. Stutchbury in our 

 Proceedings for 1841, p. 87, as mentioned above under the name 

 of Dactylocalyx pumiceus, and which has been more lately described 

 under another name by M. Valenciennes, a very fine specimen of 

 which is in my collection ; but in this sponge it is the outer surface 

 which is marked "with deep sinuosities radiating from the root to 

 the outer circumference." 



We have lately received from Dr. William MacGee of Belfast a 

 very curious specimen of a silicious sponge?, which is also allied to 

 the Dactylocalyx and MacAndrewia, but so distinct in its form and 

 structure that I am inclined to regard it as a type of a new genus, 

 which may be called 



Myliusia, 



Sponge? silicious, funnel-shaped, fixed by the base; the upper 

 surface smooth, marked with numerous minute perforations placed 

 in nearly parallel grooves radiating from the centre to the circum- 

 ference, and with numerous large, oblong, rather unequal-sized per- 

 forations, which are fringed on the lower side with a high wall of 

 a similar structure to the rest of the sponge ; these edges of the 

 cavities causing the under surface to be covered with unequal irre- 

 gular shaped tubes of nearly the same length, and more or less con- 

 fluent together : some of these tubes are simple and subcylindrical, 

 others are expanded out and more or less crumpled on the edge 

 around the cavity, so as to end in two, three, or even four, more or 

 less circular mouths. 



Myliusia callocyathes. (PI. XVI.) 

 Hah. West Indies (Dr. MacGee). 



Dr. Bowerbank informs me that the silicious spicula of this sponge 

 are very different from those of Dactylocalyx pumiceus. As he 

 is working on that subject, I leave the peculiarities for him to de- 



