PORIFERA. III. 



chelse arcuatse; they have a more or less, sometimes very strongly, curved shaft, the end-parts are 

 relatively small. The length is 0-024 0-038"', and the diameter of the shaft 0-003 0-005 mm . The 

 chelas occur numerously and rather densely in the dermal membrane. 



This species may vary somewhat, especially with regard to the size and shape of the chelae; 

 it is most characterised by the fusiform tornota, and this character in conjunction with the shape of 

 the acanthostyli distinguishes the species with certainty. 



Locality: Station 54, 63 08' Lat N., 1 5 40' Long. W., depth 691 fathoms; station 98, 65 38' Lat. N., 

 26 27' Long. W., depth 138 fathoms. The localities are situated in the Denmark Strait and South 

 of Iceland. 



16. H. perforata n. sp. 



PI. Ill, Fig. 4, PL VII, Fig. 3. 



Incrusting; surface somcivhat hispid; main skeleton rather dense. Spicula: megasclera; the 

 skeletal spicules acanthostyli with a very small or no head, entirely spined, or the longer with a smooth 

 apical part, 0-080 0-53, not 'divided into two groups; the dermal spicules slender tornota orij8<r22 mm ; 

 microsclcra chelce arcuatcz, -very varying in size, 0-021 0-054""". 



This species grows chiefly on Brachiopods, as well on dead shells as on living specimens; 

 we have in all sixteen specimens, thirteen of which grow on Brachiopods; the other three grow re- 

 spectively on a Bryozoon, a worm-tube and a Peeien-datXL The greatest extent to which the species 

 reaches is about i6 mm , and the thickness is not beyond 0-5 mm . The colour (in spirit) is brownish 

 yellow to dark greyish brown. The stirfacc is hispid on account of the longer styli projecting beyond 

 it. The dermal membrane is a thin and transparent film. In the membrane larger and smaller, 

 circular or oval openings are found, which are oscula and pores ; they were measured of sizes from 

 about 0-05 to 0-3 mm , but there seem to be all intermediate sizes, so that it is often not possible to 

 decide whether we have to do with incurrent or excurrent openings; the smaller openings, however, 

 were most frequently collected in groups over the subdermal cavities, but the dermal membrane was 

 much damaged and therefore the whole structure was not to be decided with certainty; probably 

 there is the difference, that the pores form sieves while the oscula are larger, single openings. The 

 somewhat close-lying, circular subdermal cavities or openings of the canals shine through the mem- 

 brane, but they are only visible by the aid of a lens. 



The skeleton. The dermal skeleton; in the dermal membrane occur the chelse numerously, but 

 somewhat scattered. The dermal spicules form bundles which stretch in an oblique direction from 

 the skeleton out to the membrane; besides, both bundles and scattered spicules are found lying hori- 

 zontally in the membrane. The main skeleton consists in the ordinary way of acanthostyli which 

 have their heads attached to the substratum; the longest of the styli pierce the membrane, the surface 

 thus getting strongly hispid, but as the largest styli are not numerous, the sponge is somewhat 

 clispersedly hispid; on the other hand the styli are in this species very dense at the base, so that 

 whether the sponge is seen in a vertical section, or the surface of attachment is seen from below, 

 the styli are seen standing nearly head by head, only here and there divided by the cavities of the 



