REPORT ON THE KERATOSA. 27 



secondary fibres, these latter also occasionally uniting tlie columns with one another, 

 the fibres themselves being thick and hard. To the diagnosis given by F. E. Schulze 

 of his Hippospongia I can add the following point, allowing an easy distinction 

 to be made between the representatives of this conjectural genus, and concerning the 

 character of the outer surface, though admitting of no examination of the outermost 

 ends of the canals perforating the body of the sponge, but still betraying their presence 

 by an alternation of thick and massive portions of the sarcode with spots where only 

 very thin membrane covering the subjacent cavities is to be found. The drawing of 

 my Hippospongia anomala given on PI. VII. will illustrate my idea. This character, 

 however, is only of practical importance. To sum up, both in Stelospongos and Hippo- 

 spongia we have to deal with porous forms, the skeletal fibres of the first genus, 

 however, admitting of a distinction into thick primary and finer secondary ones, those 

 of the genus Hippospongia being on an average all of the same size and thickness ; 

 a good distinction indeed, and further, a typical Stelospongos has a quite different 

 shape from that of a typical Hippospongia. But as stated before, the matter is by no 

 means so very simple. As to the typical Hippospongice, I found many of them (aU 

 belonging to the species Hippospongia equina) in the collection of Prof. F. E. Schulze at 

 the Zoological Institute of Graz, and I make use of this opportunity in order to express 

 my great thankfulness to Prof. F. E. Schulze for his liberality ; as to the typical 

 Stelospongos, Prof. Steenstrup of Copenhagen has been kind enough to send me three 

 specimens of it determined as Stelospongos by 0. Schmidt himself. But together with 

 these three specimens, Prof. Steenstrup sent me some other horny sponges (different 

 varieties of Hyatt's Spongia agaricina, subsp. dura) distinguished also by radial 

 columns as described before, the fibres constituting them being, however, all of the 

 same dimensions ; and again, in the Challenger Collection I find one specimen also of the 

 same character, but with fibres thick and rigid, while those of Prof. Steenstrup's specimens 

 just mentioned are fine and elastic. The skeleton of a typical Hippospongia has a 

 rather difierent appearance from that of a typical Stelospongos,^ but it is obvious that 

 if the canals perforating the body of a Hippospongia were to assume a more regular 

 disposition, we should have a skeleton in the form of numerous columns standing separately, 

 which is so very characteristic of the genus Stelospongos. This is, as we have seen, the 

 case both with regard to Hyatt's Spongia agaricina, subsp. dura, and again, atl east 

 in a certain degree, with regard to the sponge of the Challenger Collection above alluded to. 

 The first mentioned can indeed be still regarded as Hipposp)ongia, the last mentioned, 

 however, only if we enlarge the diagnosis of the genus Hippospongia in order to group 

 into it forms with thick skeletal fibres. Neither is it Stelospongos, since its fibres do 

 not admit of the distinction into primary and secondary ones. I ask, to which character 



1 Comp. Scliulze's paper on Spongklfe, Zeitschr. f. tviss. ZooL, vol. xxxii. pi. xxsv. fig. 14, and Schmidt's Spongien 

 des atlantischen Gebietes, pi. iii. fig. 13, and also my drawing PI. VI. fig. 2. 



