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



difference with regard to the structure of the skeleton ; in OUgoceras coUectrix the 

 skeleton is represented by small isolated horny trees, and there are parts in the body 

 where no skeleton is to be found at all ; in the species I am describing it is present 

 everywhere, but though a continuous network, is very often interrupted by large, enclosed, 

 foreio-n bodies. The skeletal fibres are full of fragments of spicules, sand-grains, &c. ; 

 their form, whether cylindrical or flat, as well as the size of the meshes formed by 

 them, is very variable. A portion of the skeleton ( x 2) is represented on PI. VI. fig. 

 13. The thickness of its fibres, vertical and horizontal indiscriminately, varies from 

 0-06 to 1 mm. 



Colour. — Outer surface greyish, parenchyma butter-yeUowish, skeletal fibres white. 



Habitat.— Station 208, January 17, 1875, lat. 11° 37' N., long. 123° 31' E. ; 

 depth 18 fathoms, blue mud. 



Cacospongia compacta, n. sp. (PL VI. fig. 11). 



The external shape of the single specimen representing this species in the Challenger 

 collection recalls that of Euspongia officinalis, var. lobosa, but of course this coincidence 

 is of no further consequence, the form in question showing the closest affinities to Caco- 

 spongia oligoceras just described. There are, however, the following distinctions : the 

 meshes in the former are comparatively large ; in the latter they are so very narrow that 

 the whole skeleton at first sight appears to be a compact mass (comp. PL VI. fig. 11); 

 in both cases the horny substance is scautUy developed, the chief foundation of the 

 skeletal fibres being represented by foreign enclosures, but whde the fibres of Cacospongia 

 oligoceras and its whole skeleton are friable, those of Cacospongia compacta are rigid and 

 hard. Again, when a fibre of the former is seen under the microscope, it gives the 

 impression that the taking in of foreign bodies has been influenced by the kind of 

 growth of the fibre ; they are disposed in it as if following certain laws of distribution, 

 and although overloaded with them, the fibres still possess a rather smooth surface. It 

 is a strained expression to speak of differentiated skeletal fibres with regard to Caco- 

 spongia compacta; a portion of its skeleton when magnified conveys the' impression 

 as if there were previously some sand-grains disposed in the parenchjTiia without any 

 order, and these sand-grains were latterly enveloped in a continuous mass of horny 

 substance. Here a large sand-grain, and immediately as a continuation of this thickening 

 a short piece of a typical horny fibre without any enclosures, finishing again with a new 

 similar thickeninsj. 



We are hitherto in complete uncertainty as to the systematic value of the colour" of the 

 horny substance in these and other cases. But if it be of consequence, this character alone 

 would justify the separation of both the forms compared ; in Cacospongia oligoceras it is 

 colourless, w^hile in the species I am characterising it is of an intense yellow colour. 



