iq6 PORIFERA. III. 



stretch into the wall bordering the areas and are here arranged densely and parallel, forming thus a 

 dense skeleton in the wall. In the membrane itself there are otherwise no spicules, or at all events 

 only some single, scattered ones. The main skeleton is of the common construction consisting of 

 vertical acanthostyli with the heads based on the substratum; the longest of them reach to the dermal 

 membrane or even pierce it. At the base there is a slight amount of spongin. 



Spicula: a. Megasclcra. i. The skeletal spicules are acanthostyli which are straight or 

 slio-htly curved near the base; the head is small but however generally somewhat distinctly swollen; 

 in the small spicules it is as a rule not swollen; the styli taper into a long and fine apex. The 

 spinulation is dense but the spines are somewhat small; in the longer spicules the spinulation is less 

 dense, the spines become very small and scattered outwards, and in the longest a larger or smaller 

 apical part, sometimes almost the half part, is smooth. The styli vary very much in size, but are not 

 divided into groups. The length is crio— o-so mm and the diameter of the head 0-014- 0-025 mm - 2 - T5ie 

 dermal spicules are straight or only slightly and somewhat irregularly curved strongyla; they are 

 often more or less polytylote, but they may also be quite smooth; one end is a little thicker than the 

 other, the thinner end has sometimes an elongate, more or less pronounced swelling, which is the 

 more distinct the thinner the spicules are. The strongyla may vary somewhat in the different 

 individuals, being in some considerably thicker and less slender than in others; in these thicker 

 strongyla there is no end-swelling. Some very fine developmental stages were seen which were 

 monactinal. The length is 0-22— o-2o,8 mm and the diameter 0-003— 0-007 mm - Microsclera are not present. 



Locality: Station 32, the Davis Strait, 66° 35' Lat. N., 56 38' Long. W., depth 318 fathoms; Ice- 

 land in 0fjord on the Northern coast, depth 18 fathoms (Ditlewsen) and at Hornsvig on the South- 

 east coast, depth 84 fathoms (Ad. Jensen, the cruise of "M. Sars" 1902). 



48. H. aequata n. sp. 



PI. X, Fig. 8. 



Incrusting; surface smooth. Spicula: megasclera; the skeletal spicules acanthostyli with a small 

 or no head, entirely spined, o-io — o-jo""", not divided into two grojips; the dermal spicules strongyla 

 o'2i— 0-298 """. No microsclera. 



This species grows as a thin but extended incrustation on the lower side of a Lithothamnion. 

 Its greatest extent may be estimated to about 40 mm but is in reality more, as the sponge follows the 

 irregularities on the underside of the Lithothamnion; the thickness is about o-25 mm . The colour (in 

 spirit) is whitish brown. The surface is smooth without projecting spicules. The dermal membrane 

 is thin and not separable. Oscula and pores were not observed. 



The skeleton. The dermal skeleton consists of bundles or fibres stretching from the main 

 skeleton, generally quite from the base up to the dermal membrane, at which the bundles are spread 

 in a penicillate way. The fibres have a more or less oblique direction, and when they are of some 

 length they stretch horizontally below the dermal membrane. The main skeleton is of the ordinary 

 arrangement consisting of erect acanthostyli with their heads on the substratum; the styli are some- 

 what distantly placed. At the base there is a distinct though not copious amount of spongin. 



