HALtCHONDRIA. 147 



they taper to a sharp point at the opposite extremity. They 

 are more or less curved and very brittle, so that the head is 

 either often broken away or awanting, when that end appears 

 to be simply obtuse and rounded. The animal matter consists 

 of a vast number of pellucid granules connected by a sort of 

 mucilage. WTien dried the sponge assumes a silky appearance 

 from the projection of the points of the spicula beyond the sur- 

 face. 



In habit and compactness of texture this sponge is a Tethea, 

 and, like the species of that genus, it is also covered with a dis- 

 tinct skin, but the disposition of the spicula is different, and 

 there is no central nucleus. 



35. H. SBVOSA, y/attened, sessile, erect, expanded lateralh/, 

 of a very compact fleshy texture xcith a smooth unporous sur- 

 face ; spicula needleshaped. 



Plate XVI, Fig. 3, 4. 



Hab. Shores of the Isle of Man, Edw. Forbes. 



Sponge sessile, undivided, forming a much compressed crest 

 or lamina of a close compact suety texture, semitransparent, ap- 

 pearing w^hen held between the eye and the light somewhat pit- 

 ted with paler scattered spots, the surface uneven, rivose, smooth, 

 without any pores or fecal orifices. 



The only specimen of this singular sponge I have seen is 

 about three inches in breadth, one in height, and about the eighth 

 of an inch in thickness. It has small resemblance to a sponge, and 

 would have been considered an Alcyonium by Lamarck. It 

 may be compared to a portion of the fatty caul of a sheep, or to 

 a piece of suet moulded to its shape by pressure. Like the H. 

 Ficus it consists almost entirely of siliceous, rather long needle- 

 shaped spicula, compacted and crossed in every direction, and 

 held together by a gelatinous membrane. The surface of a 



