220 THE VOYAGE OF H.M.S. CHALLENGER. 



Localities.— Station 73, June 30, 1873 ; lat. 38° 30' N., long. 31" 14' W.; off the 

 Azores; depth, 1000 fathoms; bottom, Pteropod ooze; bottom temperature, 39°'4. 

 Five specimens. 



Station 184, August 29, 1874; lat. 12° 8' S., long. 145° 10' E.; south-east of Cape 

 York; depth, 1400 fathoms; bottom, Globigerina ooze; bottom temperature, 36°"0. One 

 specimen. 



Trichostemma irregularis, Ridley and Dendy (PI. XLIII. figs. 4, 4a, 5). 



1886. Trichostemma irregularis, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 489. 



There are in the collection two specimens of this species which differ considerably from 

 one another in external appearance. The one (PL XLIII. figs. 4, 4a), which is probably 

 the normal form, has its parts arranged very much as in Trichostemma sarsii. In shape 

 it closely resembles an inverted mushroom without the stalk. The convex, lower surface 

 is protected by a thatch-like covering of very large spicules, which radiate upwards and 

 outwards from its centre, and form a thick, irregular fringe round the free margin. The 

 upper surface is slightly concave, strongly hispid, and bears a considerable accumulation 

 of foreign dirt. It also bears a few, irregularly scattered, small, jDapilliform processes 

 which may be oscular tubes. The specimen is about 1 7 mm. in diameter and 8*5 mm. thick 

 in the centre. (The second specimen (PL XLIII. fig. 5) appears to be abnormal in shape ; 

 it is of about the same size as the first, but the upper surface is strongly convex and the 

 lower slightly concave, and the long, projecting spicules are also very irregularly arranged, 

 projecting almost at right angles all over the lower surface.) Colour in spirit dirty 

 yellow. Texture fairly firm but rather spongy. Loiver surface, in normal specimen, 

 radiately fibrous, upper surface strongly hispid. Oscula (? several, on the upper surface, 

 on the summits of papilliform projections). 



Skeleton. — Normally arranged as in Trichostemma sarsii; the projecting spicules of 

 the ectosome, on the upper surface, however, project for a very much greater distance than 

 in that species, the portions outside the sponge being long and of hair-like fineness, 

 sometimes even flexuous. 



Spicules. — Megasclera ; all either tylostylote or subtylostylote, but of most variable 

 length ; the spicules of the ectosome and of the interior of the sponge are much larger and 

 slenderer than in Trichostemma sarsii ; the former often projecting for as much as 1 mm. 

 beyond the surface, whUe the latter commonly measure about 0"5 by 0"012 mm., but are 

 often much larger. The large external spicules seem to be of about the same size as 

 in Trichostemma sarsii ; their heads are very feebly developed. 



In appearance this species is very much clumsier and coarser than the foregoing, the 

 upper cortical and internal spicules are larger, and there seems to be more than one 

 osculum. 



