REPORT ON THE MONAXONIDA. 63 



minute, are of the Esperella type. It affords a striking example of the way in which 

 Monaxonid sponges from very deep water tend to assume a definite, symmetrical external 

 form. 



Espei^ella mammiformis, Eidley and Dendy (PI. XIV. figs. 5, 6 ; PI. XV. 

 figs. 1, 18, 18a). 



1886. Esperella mammiformis, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 337. 



Sponge (PI. XIV. figs. 5, 6) sessile, hemispherical, usually with flat base, by which 

 it is attached to stones, and a slight, free, projecting rim all round. At the top are one 

 or two (usually only one) short, slender projections, bearing the oscula at their summits. 

 Size n mm. in diameter across the base. Colour in spirit pale greyish-yellow. 

 Texture soft and stringy. Surface even, but rather rough owing to the presence of 

 numerous foreign bodies, Foraminifera, &c. Dermal membrane thin, transparent. 

 Pores; a few only have been found, here and there, about 0"04 mm. in diameter. 

 Oscula, usually one only, at the summit of a short tubular projection (PI. XIV. figs. 

 5, 6, o). One specimen had two such oscula. 



Skeleton. — (a) Dermal; a reticidation of loose spiculo-fibre, comjDosed of long stylote 

 sj)icules. (6) Main; this is arranged in a radiate manner; starting from the centre 

 of the circular base, fibres radiate in every direction except downwards. The base 

 itself thus acquires a stellate appearance, having a number of bands of spiculo- 

 fibre radiating from its centre to its circumference like the spokes of a wheel. Other 

 fibres radiate from the same point to every part of the surface of the sponge ; as they 

 approach the surface each breaks up into a brush of divergent spicules, which spread out 

 and terminate in the dermal layer, to which they give suj)port [cf. the similar aiTange- 

 ment in Esperella murrayi). In addition to the fibres just described there appear to 

 be some poorly-developed secondary fibres which cross the main ones more or less at 

 ri2;ht ansrles. 



Spicules. — (a) Megasclera; of one kind only, viz., long, smooth, slender styli 

 (PL XV. fig. 1), sometimes showing a tendency to develop heads, as in so many 

 Esperellse ; usually quite straight and tapering gradually to a very fine point ; size 

 about 1 mm. by 0'019 mm. The spicule also tapers a little towards the base. (6) Micros- 

 clera ; of one kind only, viz. , palmate anisochelae, with the front palm much rounded ; 

 length of spicule 0'072 mm.; breadth of large end 0'034 mm. The shape of these spicules 

 is very characteristic (vide PI. XV. figs. 18, 18a); smaller ones also occur, probably 

 young forms of the larger. 



Tliis is a very beautiful little species and affords another good example of a deep-sea 

 sponge with a definite external form. It is distinguished by the external form, the 



