PORIFERA. III. 



mental stages of the dermal spicules were seen in small numbers, they show that these spicules are 

 diactinal from the first beginning, b. Microsclera; these are chelae arcuatae; they have an evenly 

 curved shaft, the terminal parts are relatively small, and the alse are somewhat triangular; the length 

 is 0-034 0-040 mm ; the shaft is not cylindrical but a little flattened, the thickness is in relation to this 

 0-003 0-005 mm . The chelae occur through the whole sponge and outermost in the dermal membrane; 

 they are especially numerous in the pore-membranes. 



Locality: Station 18, 61 44' Lat. N., 30 29' Long. W., depth 1135 fathoms; station 46, 6i32'Lat. N., 

 11 36' Long. W., depth 720 fathoms; station 64, 62 06' Lat. N., 19 oo' Long. W., depth 1041 fathoms; 

 station 85, 63 21' Lat N., 25 21' Long. W., depth 170 fathoms. The localities are situated in the 

 southern part of the Denmark Strait, South of Iceland and between Iceland and Faroe Islands. 



Geogr. distr. The species was described by Bowerbank from Scotland, depth 96 fathoms; Top- 

 sent 1. c. records it from the Azores in depths of 448, 620, 756 and 1200 fathoms. It seems thus to 

 have a very wide bathymetrical range, from 96 to 1200 fathoms. 



22. H. simillima n. sp. 

 PI. Ill, Fig. 7, PI. VII, Fig. 9. 



Incmsting ; surface smooth, bearing small oscular papilla and very low, poriferous Tvarts, both 

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

 styli with a small or no marked head, divided into two groups, large, only spined at the base, 0-41 

 0-65""", small, nearly spined in the zvholc length, o-i6o-i^ mm ; the dermal spicules oxca %vith inter- 

 mediates to tornota, o-j2 0-4?"""; microsclera strongly curved chela arcuatce 0-028 



Of this species we have several specimens of various sizes, growing on larger and smaller 

 pebbles, shells, Brachiopods and tubes of Placostegus tridentatus. They are present in the material 

 in all sizes from quite small up to an extent of 30 mm ; the thickness is at most 0-7 ram . The colour 

 (in spirit) is white to greyish white. The surface is smooth, without projecting spicules; other- 

 wise it may have a somewhat wrinkled appearance on account of the papillae and impressed areas 

 to be mentioned hereafter. The dermal membrane is a thin, but distinct and separable membrane; it 

 rests on the skeleton below and is densely filled with chelae, but has no proper skeleton of horizontal 

 dermal spicules. Oscula and pores: in the somewhat large and well developed specimens oscula are 

 always found, they are conical papillae with a simple opening at the summit. The pores are also 

 limited to certain areas, which may be described as very low, broad warts, somewhat recalling 

 the structures in Inflatella viridis. They are bounded by a low wall, being generally lower on one side 

 than on the other, the wart lying down towards the surface; the pore-membrane closes the opening 

 and forms a sieve, it is densely filled with chelae. The pore-areas may be of various, generally 

 relatively large diameters, up to 3"'"'. When the sponge is examined with a lens, the pore-areas are 

 only seen with difficulty; as they are so very low the pore-membrane is always sunk down on the 

 tissue below and the pores not to be seen, and therefore the only thing seen is a circular, depressed 

 area, surrounded by a sharp edge. 



The skeleton. The dermal skeleton; the dermal spicules form bundles and short fibres stretching 



