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



membrane fairly distinct, thin and transparent. Oscula (?). Pores scattered or in 

 irregular groups. 



Skeleton. — («) Dermal ; composed of thickly strewn, spined styli and fusiform oxea, 

 the former sometimes predominating and the latter sometimes collected into distinct 

 bands of fibre, (b) Main; composed of stout ropes of spined stylote spicules, abun- 

 dantly echinated by numerous other spined styli apparently of the same kind. These 

 fibres are not very regularly disposed and appear to originate from any foreign body 

 which may form a convenient base, from which they radiate towards the surface, often 

 branching in their course. In addition to these fibres, abundant, loosely scattered, spined 

 styli occur. 



Spicules. — (rt) Megasclera; (1) small, usually curved, sharply pointed, entirely and 

 strongly spined styli, varying in size from O'l by O'OOS to 0'16 by O'OIS mm. We 

 have not been able to satisfy ourselves that there are really two distinct kinds of spined 

 styli, although great variation in size occurs. (2) Fusiform oxea ; slender, and tapering 

 gradual^ to a very sharp point at each end; size about 0"175 by 0"0048 mm.; these 

 spicules are probably homologous with the dermal spicules of tj^iical Myxillie. (b) 

 Microsclera; of one kind only, viz., tridentate isochelas, with very strongly curved shaft, 

 length about 0-015 to 0-02 mm. 



The Challenger variety difiers from the British form chiefly in the possession of a 

 more tapering oxeote spicule and a stouter isochela. 



This sjiecies is very aberrant in its skeleton arrangement, resembling Myxilla frondosa, 

 nobis, in this respect, and forming a connecting link between Myxilla and Plumo- 

 Jialichondria. It is only doubtfully that we include it in the former genus. 



Locality. — Ofi" Bahia, shallow water. One specimen and a fragment. 



Genus Clathria, Schmidt (Pis. XXVIIL, XXIX., XLVIL). 



1862, Clathria, Schmidt, Spong. Adriat. Meer., p. 57. 

 1870. Teimcia, Schmidt, Spong. Atlant. Gebiet. p. 56. 



Of various form, generally erect ; possessing usually a well-developed horny fibre 

 cored by stylote spicules and echinated by smaller spined styli. Typical microsclera 

 small palmate isochelse ; no special dermal crust of spicules as in Rhaphidophlus. 



Schmidt's original diagnosis {loc. cit.) runs as follows : — " Halichondrise maxime 

 ramosse, ramis in modum clathrorum ssepissime inter se connexis. Substantia aciculas 

 involvens subcornea, elastica dum aqua est imljuta, fragilis et fere friabilis, dum spongia 

 est exsiccata. Rete microscopicum spiculorum, ista substantia conjunctorum maxime 

 irregulare." 



This, though very true so far as it goes, is obviously insufiicient, and Vosmaer ' in 



> 1 Notes from the Leyden Museum, vol. ii. p. 149. 



