SPONGES. L53 



and echinated abundantly by similar oxea projecting from the fibre singly or in small 

 groups. The diameter of the dermal fibre is about 0'024 millim. ; of the meshes 

 between the fibres about O'lG millim., but variable. 



Spicules. Rather short, slightly curved, gradually sharp-pointed oxea (Plate X., 

 fig. 4), measuring about 0"084 millim. by 0*004 millim. in the dermal skeleton and in 

 the tertiary fibres of the main skeleton, but becoming more or less vestigial in the 

 other fibres. 



R.N. 342 (Stat. V., ofFChilaw, 10 fathoms). 



Ceraochalina reticutis, u. sp. Plate X., fig. 8. 



The type specimen (R.N. 58) forms an agglomeration of short, irregular, sub- 

 cylindrical or angular branches, slightly anastomosing with one another and branching 

 with great irregularity. The branches vary greatly in diameter, from about 4 millims. 

 to about 11 millims., and have a slightly nodose appearance. The entire mass 

 measures about 80 millims. in greatest breadth. Vents small (about 1 millim. in 

 diameter), but conspicuous and with slightly projecting margins ; scattered abundantly 

 and sometimes in ill-defined longitudinal series. The dermal membrane is parchment- 

 like, and under a pocket lens appears very finely and regularly reticulate in triangular 

 meshes, which are the coarser meshes of the dermal skeleton composed of dark brown 

 spongin fibre. Texture (in spirit) compressihle, very resilient, tough ; colour dark 

 brown. 



The main skeleton is a fairly regular, sub-rectangularly meshed network of strong 

 horny fibre. The principal fibres run longitudinally through the branches, sub- 

 dividing as they go and curving outwards to the surface. They measure up to about 

 - 08 millim. in diameter, and contain a considerable number of slender vestigial 

 spicules, irregularly and multiserially arranged. The secondary fibres are about as 

 thick as the primaries, but contain fewer spicules (which are also vestigial). The 

 meshes of the main skeleton reticulation vary a good deal in size ; averaging, say, 

 about 0*33 millim. in diameter. 



The dermal skeleton (Plate X., fig. 8) is a very well developed, close, polygonal- 

 meshed reticulation of horny fibre containing only a very few slender spicules scattered 

 here and there. The fibres of which this reticulation is made up are of two principal 

 sizes : () stout, about 0'03 millim. to 0"05 millim. in diameter, radiating from the 

 ends of the primary fibres of the main skeleton and forming the coarser triangular- 

 meshed reticulation visible under a pocket lens; (b) more slender, hut very variable 

 in diameter, forming a very close-meshed but irregular reticulation in the meshes of 

 the coarser reticulation. A large number of well developed spicules may be irregu- 

 larly scattered in the dermal membrane outside the horny fibres of the dermal 

 skeleton. 



Spicules. Oxea ; varying greatly in degree of development : in the horny fibres 

 very slender and vestigial (Plate X., fig. 8, v.s.), but often well developed in the soft 



x 



