'28 THE VOYAGE OF H.M.S. CHALLENGER. 



have we to give the preference, to the cliflferentiation of the fibres into primary and 

 secondary ones, or to their thickness and rigidity ? Through my Hippos2)ongia anomala, 

 and indeed many other still unknown forms, the genus Eusjyongia is very closely allied 

 to the genus Hippospongia ; through Cacospongia moUior, 0. Schmidt, it is not less 

 closely allied to the true CacospongicB ; both Cacospongia and its special modification 

 the genus Stelospongos being connected with typical Hippospongice by means of forms 

 similar on the one hand to my Cacospongia intermedia, and on the other to Stelosiwiigos 

 friahilis and Sjwngia agaricina, subsp. dura, Hyatt. The reader sees that in these 

 genera we meet the same circulus vitiosits as in speaking of the mutual afiinities of 

 difi"erent families of the group Keratosa, and that the classifier in numerous cases has 

 no other guidance than his own individual opinion. A quite analogous phenomenon we 

 find also with regard to the next genus. 



Coscinoderma. 



This genus was created in the year 1883, and defined by Mr. Carter,^ by many 

 characters of which, however, only one can claim the designation of a generic one, namely, 

 the uniformity of the skeletal fibres as in Hip>pospongia , these fibres not admitting of 

 the distinction into primary and secondary ones, being all of the same thickness, and not 

 forming polygonal meshes but such as may be compared with wool-whorls. Of course the 

 system of internal canals, so very characteristic of Hippospongia, is not to be found here. 

 Mr. Carter established his genus for only one species, Coscinoderma laniiginosum, and 

 characterised it, inter alia, by a specially differentiated dermal membrane full of foreign 

 bodies, the fibres of the skeleton being almost free from any enclosures, and by the 

 evenness of the external surface. In the Challenger Collection I find a specimen with the 

 dermal membrane, like that of Coscinoderma lamiginosum, full of foreign enclosures, 

 and in general, apart from the colour of the skeletal fibres, just of the same properties as 

 the above-mentioned species, with very fine skeletal fibres, and forming no polygonal 

 meshes. But the outer surface of this specimen proved to be uneven, owing to the 

 sharp-pointed dentieulations of the skeleton. Further, I find a specimen whose dermal 

 membrane cannot be easily drawn ofi", whose skeleton meshes are polygonal, but which 

 shows on the surface of its skeleton the same dentieulations, corresponding with sharp- 

 pointed networks of the skeletal fibres, precisely as in the specimen I have just spoken 

 of, but whose fibres are all of the same thickness, their colour — of a paler shade in the 

 specimen before mentioned — being, as in Coscinoderma lanuginosum, rather brownish, and 

 almost entirely devoid of any foreign enclosures. And finally, I find a specimen 

 quite difi'erent from those before mentioned in its external shape, with fibres cored 

 with foreign bodies, but still all of the same thickness. Are all these forms really so 

 closely allied to one another as to be united into one genus ? 



' Ann. and Mag. Xat. Hist., ser. 5, vol. xii. p. 309, 1883. 



