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



horny sponges do really belong to the Keratosa, that, e.g., Dysidea antiqua. Carter,' from 

 the Carboniferous system, is really a horny sponge and not a worm-tube or something of 

 that kind, in a word, should we feel certain that Keratosa is a palseontologically old group, 

 of course we should regard Hippospongia, Euspongia, &c., as representing each a 

 subgenus, and pay but little attention to the existence of forms like Velinea gracilis, Vos- 

 maer, or my Cacospongia intermedia conditioning the circulus vitiosus above mentioned. 

 But this is precisely the question to be answered; it is but too possible that Keratosa is a 

 very recent group, and in this case the many-sidedness of their affinities may be explained 

 by their very high variability, in which case only specific and varietal importance must 

 be ascribed to the characters we regard now as of subgeneric or even generic value. 

 Prof. F. E. Schulze established a new genus OUgoceras ; he told me that all specimens of 

 his OUgoceras collectrix were found between stones in a position which renders the 

 presence of a special supporting skeleton superfluous ; it is to be asked whether the loss 

 of this latter is immediately realisable or not. It is, in one word, necessary to expi*ess 

 more or less approximatively the proportion between the stability of these and other 

 characters and their mutability, i.e., their faculty of conforming to existing influences. 

 His genus Hippospongia, F. E.. Schulze characterises by the presence of numerous 

 channels, i.e., cavities breaking through the body of its representatives in diS'erent 

 directions. That this property is due to the necessity of enlarging the outer 

 surface is perfectly clear ; it is again to be asked whether this character can be 

 adopted in a short space of time. Mr. Carter established a genus Coscinoderma, but with 

 the diagnosis he gave ^ to it in his last paper the genus is not adoptable : " Sieve-like 

 incrustation, composed of foreign bodies uniformly foraminated and continuously spread 

 over the surface, whose evenness is not disturbed by the usual polygonal projection of the 

 subdermal fibre. Fibre fine, woolly." Should we follow it we should have this genus 

 represented but by the single species lanuginosum. I widened the diagnosis and de- 

 scribed as Coscinoderma also Coscinoderma altum, characterised by comparatively thick 

 skeletal fibres, in most cases cored with foreign enclosures. The type-specimen of 

 Coscinoderma possesses very fine fibres, all of the same diameter ; the skeletal fibres of 

 all CacospongicB are thick, and usually overloaded with foreign bodies ; they admit, 

 however, of the distinction of primary and secondary ones. Coscinoderma altum has 

 thick fibres cored with foreign bodies, but all its fibres are of the same size. Ought I 

 to class the form in question in the genus Coscinoderma or in that of Cacosp)ongia ? 

 Ought we to ascribe to the difierentiation of the fibres into primary and secondary ones a 

 higher systematic consequence than to their equal size ? The reader who has perused 

 my description of the Challenger specimens will find there such alternatives at every 

 step. And to sum up, so long as we possess no statements as to the stability of the 

 characters of the horny sjDonges we shaU have no natural arrangement of them. There 



I Ann. and Mag. Nat. Hist., ser. 5, vol. i., 1878, p. 139. ^ Ibid., February 1884, p. 129. 



