102 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus Meliiderma,'^ n. gen. (Pis. XX., XXL). 



1886. Cliondrocladia {/ ars), Ridley aud Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 3i4. 



Sponge stipitate. Megasclera stylote to tylostylote. Microsclera, isochelse of the 

 ordinary Cho7idrocladia form, to which may be added sigmata. In addition to these 

 forms of spicules a sjDecial protective spicule occurs encrusting the stem, each spicule 

 consisting of a slightly expanded base of attachment, a constricted neck, and a fusiform, 

 outwardly projecting shaft, terminating in a pointed apex {vide annexed woodcut, Fig. 6). 



This genus stands in much the same relation to Chondrodadia as does Axoniderma 

 to Cladorhiza, having, like Axoniderma, developed a special spicule for external 

 defensive purposes. The form of the extra spicule is, however, totally different in the 

 two cases ; and in Meliiderma it appears to be confined to the stalk, while in Axoni- 

 derma it is most abundant in the body of the sponge. In both these cases it is very 

 difficult to say whether the extra spicule ought to be classed amongst megasclera or 

 microsclera ; for the sake of convenience both will here be regarded as microsclera, 

 though standing on quite a different footing from other microsclera. The form of 

 the extra microsclera in Meliiderma stipitata is as j'et unparalleled. From their re- 

 semblance to spears or darts we have derived the generic name. 



Meliiderma stipitata, Ridley and Dendy (PL XX. fig. 11 ; PI. XXI. figs. 6, 6a, 6&, 

 Qc, 14). 



1886. Chondrodadia stipitata, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 344. 



Sponge (PL XX. fig. 11) consisting of a spherical head perched on the end of a 

 long stalk, which in the one perfect specimen is much bent. Diameter of head about 

 12 mm. Length of stalk in the perfect specimen, 25 mm., diameter about 2 mm. 

 At the base the stalk terminates in a flattened expansion which is firmly attached to a 

 fragment of black volcanic cinder. Colour in spuit pale yeUow. Texture of head 

 soft. Surface hispid. Dermal membrane fairly distinct. 



Skeleton. — There is no dermal reticulation, and the main skeleton consists chiefly of a 

 very dense band of spiculo-fibre, forming the greater part of the stem ; this penetrates the 

 spherical head for a short distance and then expands slightly into a knob-like extremity, 

 from which radiate thin bauds of loose spiculo-fibre in aU directions, running vertically 

 to the surface. Numerous spicules jaroject for some distance beyond the surface of the 

 sponge, giving to it its hispid appearance. 



Spicules. — (a) Megasclera ; of one kind only, viz., long tylostyli (PL XXI. figs. 6, 

 6a, 66, 6c), often a little crooked, measuring up to 2-2 by 0'038 mm.; head, as a rule, 

 only very slightly indicated, apex sharply pointed ; the spicules are broadest in the 



1 Greek litkla,, a spear, and otj^ta, the skin. 



