PORIFERA. III. 



107 



SpicTila: a. Mcgasdera, i. The skeletal spicules are somewhat slender acanthostyli ; they 

 are straight or, the longer of them, slightly curved and these latter have a small head-swelling; the 

 small styli have a very slight head-swelling or often no swelling at all. The styli are somewhat 

 densely spined with small spines, and they are all, both the large and the small, spined in the whole 

 length; the spines are relatively largest in the small styli. The length is o-io crjo" 1 " 1 and the 

 diameter at the base 0-012 o - oi7 mm . The styles are not divided into two groups. 2. The dermal 

 spicules are strongyla which have one end a little thicker than the other, and they are slightly 

 fusiform, being a little thicker in the middle than towards the ends; they may sometimes be slightly 

 polytylote, which is especially the case with the thinner (not fully developed) forms. The length is 

 o-2i 0-298 mm and the diameter in the middle 0-004 0-007 mm . Microsclera are not present 



This species is very difficult to characterise towards the three preceding ones, but it is no 

 doubt distinct From Dujardinii it is distinguished already by the dermal strongyla, as in Dujardinii 

 there are always at all events some tylota among the dermal spicules; primitiva has longer, somewhat 

 more robust styli with somewhat stronger spines, and distinctly polytylote dermal spicules; longurius 

 finally is easily distinguished by the long styli which are smooth in a shorter or longer apical part. 

 Also the small styli without heads are characteristic for the present species. 



Locality: At Ikamiut in North Greenland. One specimen. 



49. H. dermata n. sp 

 PL III, Fig. 17, PL XI, Fig. i. 



Incrusting; surface smooth, bearing a number of conical, compressed oscular and pore-papill<e. 

 The dermal skeleton much developed, the main skeleton rather weak. Spicula: megasclera; the skeletal 

 spicules acanthostyli with a small or no head, divided into two groups, large, only spined below, o-jo 

 0-4/7""", small, spined in the whole length 0-707 o-ij mm ; the dermal spicules long strongyla o-jj 0-45""". 

 No microsclera. 



Of this species we have a couple of specimens growing on a branching Bryozoon, and one 

 growing on a stone; the latter specimen is incrusting in the common way, but the specimens growing 

 on the Bryozoon quite envelop the branches of this, and they also extend between the branches, filling 

 the interspaces with their body, which however in these places is thin and plate-shaped. The greatest 

 extent of the species is about 35"', and the thickness of the incrustation may reach 1-5 mm . The colour 

 (in spirit) is whitish or yellowish white. The surface is smooth, without projecting spicules, it bears 

 a number, smaller or greater, of conical papillae; these papillae are highly compressed and are generally 

 lying quite down towards the surface with a flat side turned upwards, and the arrangement is then 

 such, that the opening, which lies in reality in the summit, comes to lie at the summit of the side 

 of the papilla, which is turned upwards. The dermal membrane is a thin and separable film; it has 

 no skeleton proper, but the tissue lying below it, and which has horizontal fibres, is liable to be 

 separated off together with the membrane, the whole thus giving the impression of a thick and solid 

 membrane. Oscula and pores are certainly situated on the papillae mentioned; most of these show a 

 rather large opening at the summit, while some others are more pointed and conical with a small 



14* 



