186 Mr. H. J. Carter on the 



fibreless, composed of a dense mass of spicules imbedded in 

 areolar sarcode ; essentially spiculous, and growing, like all 

 other sponges, in concentric layers. Surface even, smooth, or 

 asperous, not corticate. Colour grey when fresh or wet, yel- 

 lowish white or brown when dry. Vents pustular, uniformly 

 scattered, singly or in little groups, on the inner side of the 

 wall only. Branched excretory canal-system well defined, 

 although small in calibre, corresponding in this respect with 

 the compact structure of the sponge. Pores general, in the 

 sarcodic interstices of the dermal layer. Spicules of two kinds 

 for the most part, viz. skeleton- and flesh-spicules. Skeleton- 

 spicule of three forms, viz.: — 1. The surface-spicule, consisting 

 of a horizontal head and vertical shaft, the latter directed in- 

 wards. Head consisting of three round smooth arms, spread 

 out horizontally and symmetrically furcated, amidst the flesh- 

 spicules of the surface ; or with three flattened, irregularly bi- 

 furcated and sinuous arms ; or with the same denticulated on 

 the borders ; or united together laterally, so as to form a disk 

 more or less deeply fissured on the margin, or subcircular ; 

 or with the arms sinuously branched, and the branches more 

 or less tubercled, the tubercles simply round or two- or three- 

 spined. Shaft for the most part smooth, straight, round, and 

 pointed, presenting, where it joins the head, a trifid division 

 of the central canal, whose arms (being short, equal in length, 

 and symmetrically disposed) form a very characteristic feature 

 on the surface and in the interior, whereby the original direc- 

 tion of the spicule can be ascertained. 2. Body- or staple spi- 

 cule of the mass, consisting of a horizontal head and vertical 

 shaft, which thus seems to mark the concentric layers of 

 growth ; but otherwise it is so altered from the original surface- 

 spicule that the shaft becomes marrow-bone-like in form, and 

 the arms not only bifurcated and sinuous, but so intensely and 

 irregularly branched and filigreed, and so intimately and in- 

 tricately interlocked with each other and the branches of the 

 inner end of the shaft of the next layer (which, to a certain 

 extent, so simulates the head in this respect as to be almost 

 undistinguishable from it), that, in the mass, the bodies of the 

 shafts respectively can only be recognized by the comparatively 

 open interval which they form between the lines of dense in- 

 terlacement caused by the intermixing of their almost equally 

 branched extremities — while, when the mass is broken up, 

 the shaft can only be identified by the trifid central canal before 

 mentioned, when this is visible. At the same time, this trifid 

 canal often presents itself in such a position as to indicate that 

 either the spicules of the mass become more or less confusedly 

 mixed up together like those of Pachastrella, or that the shafts 



