PORIFERA. III. 67 



but the dermal spicules are polytylote strongyla and the chelae are very strongly curved; it is also 

 related to H. similis, but it is, as mentioned under this species, distinguished by the small styli being 

 straight, and by differences in the dermal spicules and the chelae; also the styli mtymilis are distinctly 

 divided into two groups. 



Locality: Station 7, 63 13' Lat. N., 15 41' Long. W., depth 600 fathoms, and at 61 09' LaL N., 

 7 54' Long. W., depth 180 fathoms, (Ad. Jensen, the cruise of "M. Sars" 1902). Two specimens in all. 

 The localities lie South of Iceland and West of the Faroe Islands. 



21. H. occulta Bow. 

 PI. Ill, Fig. 6, PL VII, Fig. 8. 



1874. Flymedesmia occulta Bowerbank, Mon. Brit. Spong. II, 250, III, PI. LXXIX, figs. 911. 



1894. Desmacidon occultum, Hanitsch, Trans. Liverp. Biol. Soc. VIII, 180. 



1894. Hymeraphia occulta, Topsent, Rev. Biol. du Nord de la Fr. VII, 12 et 21. 



1904. Leptosia occulta, Topsent, Resultats des camp, scient. du Prince de Monaco, Fasc. XXV, 186, 



PI. XV, fig. i. 



Incrusting; surface smooth, generally with a number of papillce, bearing oscnla and pores, and 

 with a dense skeleton of dermal spicules in the wall. Spicula: megasclera; the skeletal spicules acantho- 

 styli with a small, but distinct head, divided into two groups, larger, only spined below, o-qj rip""*, 

 smaller, entirely spined, 0-119 0-26""" ; the dermal spicules tornota to oxea o-j<f o'jo""*/ microsclera 

 chela; arcuata with relatively small end parts, 0-034 0-040""". 



Of this species we have some specimens growing on stones, pebbles, small shells and one on 

 a tube of Placostegus tridentatus. Most specimens are rather small, only reaching to an extent of 

 i2 mni ; only two specimens, growing on larger stones, have a greatest extent of 18 and of 2o mm ; the 

 thickness reaches at most i""". The colour (in spirit) is whitish grey or brownish. The surface is 

 nearly smooth, but seen with a lens it shows small, punctiform projections, caused by the skeletal 

 spicules reaching the dermal membrane, but not piercing it. The surface may otherwise have a 

 different aspect; in some specimens, especially the small ones, it shows no or only few and imper- 

 ceptible papillae, but in the larger and best developed specimens the surface bears a number of 

 papillse, often rather close-standing; the papillae are conical or nearly cylindrical, and may reach to a 

 height of about i'5 mm , but the exact length cannot be given, as one side of the wall is generally 

 shorter than the other, the papillae lying somewhat down towards the surface. The dermal membrane 

 is a transparent, somewhat solid and easily separable membrane; it has an irregular skeleton of hori- 

 zontal spicules and is more or less densely filled with chelae, which form, however, no layer. Oscula 

 and pores: the papillae mentioned are both oscular and pore-papilla;. The oscular papillae are more 

 conical and tapering than the others and have a simple oscular opening at the summit; the pore- 

 papillae are broader at the tip and have here a membrane with pores. Bowerbank, who had 

 only one small specimen, does not mention papillae; Topsent, on the other hand, has perhaps 

 seen something of the kind, as he says (1. c. 186) that the sponge somewhat resembles a small 

 Hamacantha. 



9* 



