PORIFER.^. I. 47 



single, only rarely a few alongside. The whole structure forms a somewhat irregular reticular work 

 with more or less quadratic meshes. The ends of the spicules are united by a not copious mass of 

 spongin, exceedingly clear and therefore difficult to observe. 



Spicula are oxea; they are evenly tapering, and very evenly and slightly curved; they vary in 

 length from o-iS — 0-205""", the thickness is oftenest o-oii""", but may decrease to o-oo8'"'"; shorter and 

 much finer spicules occur in small numbers, and are by transitional sizes shown to be developmental 

 forms. 



This species, by its skeletal structure, is nearly allied to the preceding one, but is distinguished 

 from this latter as well by its looser consistency as by its thicker, evenly and slightly curved needles. 

 A couple of specimens from the Davis Strait have a still looser construction than the other ones. 



Locality: Station 127, north of Iceland, 66°33' Lat. N., 20-05' Long. W., depth 44 fathoms; Iceland 

 (Jap. Steenstrup); the Davis Strait, depth ca. 100 fathoms (Holm); nine specimens or fragments in all. 



10. R. heterofibrosa n. sp. 

 PI. II, Fig. 8, PI. XI, Fig. 14. 

 The form is flie typical one, an irregular cushion with a )iuinber of loiv, very little projecting 

 oscular cones. The deniial lueiiibrane thin, without spicules, the ends of the fibres projecting, so that the 

 surface is finely shaggy. Oscula are found on the summit of the oscular tubes. The skeleton is a some- 

 Zi'hat irregular netn'ork of mostly polyspicular fibres running toivards the surface, and these fibres are 

 connected by transverse spicules, single or in bundles. In the deeper parts of the sponge the skeleto)i is 

 more irregular. The spicules evenly curved oxea of a length of o-i6 — o-iyS""". 



Of this species we have one specimen, forming an irregular, lengthy cushion, which rises into 

 a number of low oscular tubes (in the specimen 8). The length of the specimen is 29""", and the 

 greatest height i5'"'". The colour (in spirit) is yellowish brown. The surface is finely shaggy from the 

 projecting spicules. The dermal membrane is thin, without spicules, and pierced by the ends of the 

 fibres. The circular oscula which are found on the top of the low cones, have a diameter of 1—2""". 

 The pores are oval or round openings in the dermal membrane, they have a diameter of 0-017 — 0-06""". 

 The oscula lead into oscular canals of the same width, on the inside of which the excurreut canals 

 open, and which pass below into wide canals. 



The skeleton consists of a somewhat irregular network of fibres, the structure being mostly as 

 in tubulosa and laxa. Most of the fibres running towards the surface, are polyspicular; they vary 

 somewhat with regard to the number of spicules of which they are composed, and upon the whole 

 they appear to be thickest and consist of most spicules in the deeper and older parts of the spouge, 

 while towards the surface they are thinner, and often consist of only a single series of spicules. The 

 spicules that are perpendicular on these fibres, do not form, or form onl\- to a small degree coherent 

 fibres; most frequently they are single, but sometimes some may be put together in bundles. In the 

 deeper and older parts of the sponge where the fibres are thicker, the skeleton is more irregular, and 

 the difference between primary and secondar}- fibres is here effaced, so that the skeleton becomes an 

 irregular net of fibres with a rather large number of spicules alongside. The ends of the spicules are 



