REPORT ON THE MONAXONIDA. 103 



middle and taper gradually towards both ends, (b) Microsclera ; (l) large Lsochelfe 

 (PI. XXI. fig. 14) with curved shaft and five prominent claw-like teeth at each end ; 

 the shaft is considerably expanded laterally near each end, but contracts again before 

 the points of attachment of the teeth. Length of spicule aljout 0-085 mm. The chelate 

 spicules are especially abundant in the dermal membrane and 

 around the embryos. (2) Slender sigmata, often contort, 

 measuring about 0'055 by 0'016 mm.; these s]3icules are com- 

 paratively scarce. (3) The spear-like spicules (vide woodcut 

 annexed) ; these are densely packed in a single layer around 

 the stalk, each with its apex projecting vertically outwards. 



Only one perfect specimen of this sponge and one damaged 

 one are in the collection ; in both of these the stalk is encrusted 

 by a thin, yellow, velvet-like layer of the densely packed, spear- 

 like spicules. At first we thought that these spicules belonged 



. . . . ™ ^"'- 6' — Meliidenna ' stipitata. 



to some foreign encrustmar sponsfe, and hence no mention of spicules encrusting the stem. 



, . . . X 400. 



them was made in our Preliminary Report, but subsequent 



examination has convinced us that they are proper to the species ; the fact of their 



occurring in both specimens being strong evidence in favour of this view. 



An interesting point about the sponge is the position in which the embryos develop. 

 In the specimen which we cut open, a number of round yellow bodies were found, each 

 enclosed in a membranous caj)siile around which the chelate spicules were lying in 

 very great numbers. These embryos were placed in a zone of tissue occupying about 

 the centre of the spherical head, and lying immediately above the expanded termination 

 of the stalk, between the bands of spiculo-fibre which radiate from it ; this being 

 obviously the position of greatest security. 



Localitij. — Station 147, December 30, 1873 ; lat. 4G° 16' S., long. 48° 27' E.; 

 between Prince Edward Island and Crozet Island ; depth, 1600 fathoms ; bottom, 

 Diatom ooze ; bottom temperature, 34°'2. Two specimens. 



Genus Desmacidon, Bowerbank (Pis. XXIIL, XXIV., XXX., XLVIL). 



1842. Halichondria (pars), Johnston, British Sponges, p. 88. 

 1864. Desmacidon, Bowerbank, Men. Brit. Spong., vol i., p. 200. 



Form various. Distinct spiculo-fibre, with a large amount of uniting spongin, 

 may or may not be present. Megasclera diactinal, oxea or strongyla ; microsclera 

 isochelse, and, at any rate usually, sigmata. 



The genus is usually made much more comprehensive than the above diagnosis 

 would permit. It has thus become unwieldy and artificial, including forms which are 

 much too dissimilar to be placed together. It was founded by Bowerbank, who gives 

 the following generic diagnosis (loc. cit.) — "Skeleton fibrous, irregularly reticulated. 



