8o 



PORIFERA. III. 



Locality; Station 85, 63°2i'Lat. N., 25°2i'L,ong.W., depth 170 fathoms; station 89, 64° 45' Lat. N., 

 27 20' Long. W., depth 310 fathoms; both localities lie in the Denmark Strait. 



Remarks: The three species Bowerbanki, truncata and latrunculioides form together with Zet- 

 land iea Bow. a group of related species; zetlandica is however distinguished from the three others by 

 possessing sigmata; truncata and latrunculioides are the two most nearly related species. A fifth species 

 which seems also to belong here on account of its uniform acanthostyli and dermal tylota is the H. 

 tcnuissima Dendy (established by the author under the generic name of Myxilld), and perhaps also a 

 sixth species must be referred to this group, viz. H. obtusata Tops., but this latter species has no 

 microsclera; its curious, obtuse acanthostyli with a little knob at the apex vary a little more than the 

 acanthostyli in the other species, from 0-13 to 0-23 rara . 



If the views about the relationship of these species are correct, and they are certainly so at all 

 events with regard to the first four species, we have an interesting example which shows, that in a 

 group of nearly related species we may have forms with chelae and sigmata, with chelae alone, and 

 with no microsclera at all. This confirms the view advanced in the introduction to the genus, that 

 it is not possible to create genera here according to the presence or non-presence of the mentioned 

 forms of microsclera. 



30. H. irregularis n. sp. 

 PL VIII, Fig. 8. 



Incrusting; surface partly smooth partly hispid. Spicula: megasclera ; the skeletal spicules 

 acanthostyli with a distinct head, the smaller spined in the whole length, the larger with a smooth 

 apical part, 0-12 — o-jo""", not divided into two groups ; the dermal spicules polytylote styli 0-298 — o-jp"""; 

 microsclera chela arcitatcc 0-040 — o-ojo""". 



This species generally forms incrustations on small stones, a couple of specimens grow on 

 shells of Astarte sulcata; the greatest extent to which the sponge reaches is about 20 mra , but most 

 specimens are smaller; three of them, which grow together on a pebble are quite small, the smallest 

 only 4 mm . The thickness is scarcely more than 0*5 mm . The species is of a somewhat irregular appear- 

 ance, because it, at all events generally, does not grow flat on the substratum but has imbedded in 

 its base some small particles and gravel. The colour (in spirit) is yellowish grey to whitish. The 

 surface is in some places smooth, in other places densely hispid from projecting dermal spicules. The 

 dermal membrane is a somewhat solid membrane, densely charged with chelse. Oseitla and pores were 

 not observed. 



The skeleton. The dermal skeleton ; in the dermal membrane the chelae are close-lying, forming 

 a layer; the skeleton formed by the dermal spicules is strongly developed; it consists of spicula- 

 bundles or fibres which stretch from the main skeleton or quite from the base up towards the surface, 

 outermost the bundles are penicillately spread and support the membrane; the spicules sometimes 

 terminate just in the membrane, sometimes they pierce it more or less. When the sponge is examined 

 from above under the microscope, fan-shaped, more or less decumbent bundles of dermal spicules are 

 therefore seen. The dermal spicules all have the pointed end turned outwards. The main skeleton 

 consists in the ordinarv wav of acanthostyli with the head-ends based on the substratum; on account 



