7 6 



PORIFERA. III. 



Of this species one specimen grows on a stone together with H. clavigcra; on the stone 

 besides grow a Polymastia and a Mesapos; another specimen is growing on a worm-tube. The 

 sponge has a greatest extent of i2 mm ; it is exceedingly thin, not over o-2'" m , and its thickness is 

 not or only slightly greater than the length of the skeletal styli. The colour (in spirit) is whitish, 

 somewhat milky. The surface is smooth, without projecting spicules. The dermal membrane is 

 very thin, transparent and not separable; it has no proper skeleton. Oscula and pores were not 

 observed. 



The skeleton. The dermal skeleton; the skeleton formed by the dermal spicules consists of 

 bundles lying irregularly between the erect acanthostyli; they are more or less horizontal, but stretch 

 up to the membrane; also some single scattered spicules are seen, but there is no dermal reticulation. 

 The main skeleton is of the ordinary structure, consisting of erect acanthostyli with the heads based 

 on the substratum; as they are of about the same length, they all reach just to the dermal membrane 

 but none of them project beyond it. I could detect no spongin. 



Spicula: a. Megasclera. i. The skeletal spicules are acanthostyli; they are of a very 

 characteristic shape and to a high degree recall the styli figured by Bowerbank for H. zetlandica; 

 they are short and robust, conically tapering and without any head-swelling; they are strongly spined 

 in their whole length; the spines at the base are radiating straight out, while the other spines are 

 directed somewhat downwards; the styli are only of one size and not much varying in length; this is 

 0-09 o-oi3 mm and the thickness at the base (the spines, as always, included) 0-021 ram . 2. The dermal 

 spicules are tylota; they are straight, somewhat thickened in the middle, and the end-swellings are 

 small; they have a length of 0-19 0-238 mm , and a diameter in the middle of 0-007 0-009 mm . D - Mtcro- 

 sclera; these are chelae arcuatae which have a somewhat curved shaft and small end-parts, the alas 

 are somewhat lobe-shaped, rounded downwards, the tooth is elliptical. The chela? have a length of 

 O-O2O 0-034""" and a thickness of the shaft of 0-0028 0-005""" respectively; the larger sizes are by far 

 the most numerous. The chelae are present in the dermal membrane in somewhat considerable numbers, 

 but not at all forming a layer. 



This species is evidently nearly allied to H. zetlandica; it has the same outer appearance and 

 skeletal structure, and the shape and dimensions of both megasclera and chelae are in close agreement 

 as also the fact that the styli are of only one form; but H.setlandica has sigmates, while the present 

 species has only chelae for microsclera. 



Locality: Station 85, 632i'LatN., 25 21' Long. W., depth 170 fathoms; further at 65 50' Lat. N., 

 26 53' Long. W., depth 208 fathoms (The Fishery investigation steamer "Thor"). The localities lie in 

 the Denmark Strait. As said above, one of the specimens grows on a stone together with several 

 other sponges and among these a specimen of H. clavigera (PI. Ill, Fig. 8 a and b.). These two 

 Hymedesmia species grow side by side and quite uniting, but they are easily distinguished from one 

 another by their characteristically different aspects, clavigcra is whitish, but appears somewhat darkened 

 on account of the black stone shining through it; it is hispid and shows the canals as darker points; 

 Bowerbanki on the contrary is of a milky colour, it has a smooth surface of a quite uniform aspect, not 

 showing canals, 



