24 



H. masoni in that it has numerous parenchymal microhexactines with smooth, 

 strongly-curved rays, but it differs, without mentioning other distinctions, from 

 this and from most other species of Eyalonema, by the presence of a hitherto 

 unknown, amphidisc-like spicule, peculiar to it, to such an extent, that I was at 

 first inclined to establish a new genus for its reception. In consideration of the 

 fact, however, that it accords with the well-known characters of the genus Eyalo- 

 nema in all other respects I have refrained from doing this. 



The body of the sponge is oval, 8 cm. long, 35 mm. broad, and laterally 

 slightly compressed. It is difficult to say whether this compression was present 

 in the living sponge or whether it has been produced j9osi mortem by pressure. 

 The oscular field has, in accordance with this compression, an oval shape. It is 

 surrounded by a low but sharp protruding margin and has a diameter of 15 mm. 

 The osculum is covered by a slightly concave sieve-plate which appears as a net 

 with large meshes composed of very thin strands. From the middle of this there 

 arises a .conical protuberance, 3 mm. thick and equally high. This protuberance 

 is the upper end of a slender central cone which traverses the space below the 

 oscular sieve-plate and to which some of the membranes separating the excurrent 

 canal-stems are laterally attached. These membranes are connected with the 

 oscular sieve-plate by thin threads. Through the fine and somewhat transparent, 

 quadratic dermal reticulation of the outer surface one can see the subdermal cavi- 

 ties and the entrances of the incurrent canals. These have regularly circular 

 transverse sections and appear, thus looked at from outside, as dark round holes 

 (pi. VI, f. 1). 



The root-tuft or peduncle is above, where it arises from the lower end of 

 the sponge-body, 4 mm. thick. The upper 12 cm. of its length are still attached 

 to the sponge. The basalia-spicules composing it are, in the upper part of the 

 peduncle, spirally twisted together pretty firmly ; below, they slightly diverge. 

 The lower end has been broken off in all of them. There is no Palythoa-crust or 

 other covering on the peduncle. 



The macroscleres of the supporting skeleton are similar to those of other 

 Hyalonema-species. The subdermal oxypentactines are on an average 20 h- thick 

 and their main ray attains on an average a length of 400-600 M . Their basal 

 rays, which form a cross, are not particularly stout, on an average 60-80 ** long 

 and sparsely covered with small tubercles. The basal part of the main ray is 

 smooth and up to 10 /^ thick. The spines are short, up to 10 f^ long, obliquely 

 situated and partly curved upwards (pi. VIII, f. 7). The pinnies of the oscular 

 sieve resemble the dermal ones. 



The diactine marginalia which surround the oscular sieve-plate are 1 mm. 

 long. The distal ray, which protrudes freely, is similar to the main ray of the 

 pinnies but considerably longer. The proximal ray, which is imbedded in the 

 sponge, is shorter and smooth throughout (pi. VIII, f. 8). There is a central 



