774 NEW GENERA OF MONAXONID SPONGES, 



tion it persists intact, with smooth, unwrinkled surface, and is 

 of somewhat corky (rather than leathery) consistency. In 

 spirit-specimens the membrane is rather fleshy in appearance, 

 and the surface of the sponge is smooth, almost glabrous. The 

 dermal pores cannot be discerned. 



An especially distinctive external feature of the species is 

 the presence, on each branch, of a more or less well-marked 

 longitudinal groove, extending along the whole or greater part 

 of its length. This groove marks the course of a main excur- 

 rent canal, which runs subjacent to it immediately beneath the 

 dermal membrane. The groove, in all probability, is not a fea- 

 ture of the living sponge, but is due to collapse of the dermal 

 membrane in consequence of contraction. 



Maceration of the sponge by means of caustic potash re- 

 moves not only the dermal membrane, but also an additional 

 layer of the sponge to a depth of about 1mm. from the surface. 

 This is owing to the almost complete absence of spongin in the 

 outer portion of the main skeleton. The skeleton which re- 

 mains is a rather coarse-textured reticulation of yellowish-grey 

 fibres, harsh to the touch; it shows no trace of the longitudinal 

 groove which is so conspicuous a feature of the intact sponge. 



Skeleton. — Examined microscopically in longitudinal median 

 section (of an unmacerated branch of the sponge) the main 

 skeleton presents three usually fairly well-marked regions, viz., 

 a central, an intermediate, and a subdermal. The central re- 

 gion (PI. xxxvi., fig. 2), occupying the whole interior to within 

 from 1 to 1.5mm. of the surface, consists of an irregular, rather 

 wide-meshed reticulation of brownish yellow, multispicular 

 spongin-fibres, — with the main fibres running more or less near- 

 ly longitudinally (the more peripherally situated ones, how- 

 ever, gradually trending surfacewards), and connected together, 

 in irregular fashion, both by transverse fibres and by inoscula- 

 tion among themselves. From the outermost fibres of this re- 

 gion, short fibres branch off, which run directly outwards to the 

 surface in a direction usually not far from perpendicular 

 thereto; these, which may be termed the radial fibres, are (ex- 

 cepting for an extremely short distance beyond their origin) 

 apparently entirely devoid of spongin; are unconnected by 

 transverse fibres; and, after a short course (throughout which 

 their spicules are arranged compactly side by side), subdivide 

 to form each a widely-outspread, usually rather dishevelled 



