258 PERCY SLADEN TRUST EXPEDITION 



The cortex is about 0"2 mm. thick and is sharply differentiated into two layers — an 

 outer layer forming about four-fifths of the ^^hole and so densely charged with tangentially 

 placed aspidasters, arranged in several layers, that it is impossible to make out its 

 histological characters ; and an inner layer, forming the remaining fifth, composed of 

 fibrous tissue. Both layers contain numerous pigment cells, which, in the fibrous layer, 

 are elongated in the same direction as the fibres, i.e. parallel to the surface. A few 

 pigment cells also occur in the outer part of the choanosome. 



The scattered inhalant pores lead each into a very well-defined chone, subcylindrical 

 in shape but widening out somewhat as it penetrates the cortex, the bottom of the chone 

 being at about the junction of the outer and inner layers of the cortex. A rather thick 

 sphincter diaphragm, formed from the inner, fibrous layer of the cortex, separates the 

 chone from the subcortical crypt into which it opens. The subcortical crypts are 

 irregular spaces which unite together to form wide inhalant canals running almost 

 vertically inwards. 



The choanosomal ground-substance is compact and finely granular ; the flagellate 

 chambers are subspherical, close-packed, about 0"024 mm. in diameter. 



It will be seen that our sponge agrees very closely with SoUas's re-description of the 

 type [1888]. The chief distinguishing feature of the species is evidently the large 

 oxyaster. 



Previously known Distribution. Fremantle, Western Australia (Carter). 



Register No., Locality, &c. cii. 2, Amirante, 18.10.05, E. 25, 44 — 20 fathoms. 



17. Erylus proximus n. sp. 

 (Plate 47, fig. 5.) 



The single specimen consists of an irregular mass of Siliquaria shells and sponge 

 inextricably mixed together; the whole measuring about 65 by 36 by 25 mm. The entire 

 mass is somewhat flattened dorsoventrally, but the surfaces are very uneven and irregular, 

 with portions of the Siliquaria projecting freely at frequent intervals. What was pre- 

 sumably the lower surface is penetrated by numerous minute, singly scattered, dermal 

 pores, widely open, commonly with distinct whitish margins ; numerous minute whitish 

 specks scattered singly over the upper surface represent similar pores in a closed condition. 

 A few open vents, about 1"5 mm. in diameter, occur singly on prominent parts of the 

 upper surface. The colour of the upper surface (in spirit) is purplish or brownish grey ; 

 of the lower surface greyish yellow. 



The main skeleton is a confused interlacement of large oxea, with a few short-shafted 

 trigenes beneath the dermal crust. Some at any rate of the trieenes have their cladi 

 extended paratangentially beneath the surface. There is a thin dermal crust formed of 

 the thin, plate-like aspidasters, which also occur scattered abundantly in the choanosome. 



Spicules : — (1) Short-shafted trisenes (Plate 47, fig- 5 a) ; much resembling calthrops, 

 but with the cladi extended almost at right angles to the shaft ; cladi may be a little 

 longer or a little shorter than the shaft. Shaft and cladi sharp-pointed, stout or slender ; 



