THE 



VOYAGE OF H.M.S. CHALLENGER 



ZOOLOGY. 



REPORT on the Keratosa collected by H.M.S. Challenger during the years 

 1873-76. By N. Polejaeff, M.A. of the University of Odessa. 



INTRODUCTION. 



The Keratose Sponges do not belong to the deep-sea fauna ; it is therefore not 

 surprising that the number of forms brought home by tlie Challenger Expedition does 

 not exceed the comparatively small number of thirty-seven (twenty-one new, three 

 undeterminable). But if not numerous, the collection is still very interesting, embracing 

 as it does almost all the genera of the horny sponges hitherto distinguished, and most of 

 the specimens being in a very good state of preservation. 



Entering upon their classification and description, I feel myself in a position rather 

 different from that which I occupied some months ago when writing about the Challenger 

 Calcarea. For iu this latter case I had to deal with but one elaborate system (that of 

 Haeckel), and my task consisted simply in the reconciliation of Haeckel's systematic 

 arrangement with the modern state of spongiological knowledge. In the group 

 of Keratose Sponges the classifier meets with many detailed systems, constructed in many 

 instances upon radically different principles. My first task is consequently to show 

 which of the existing systems is to be most recommended, and with what modifications. 

 There are two ways of doing this. One way might be called " historical," and would 

 consist of a critical discussion in chronological order of all the systems of the horny 

 sponges we possess ; the second might be called " morphological," and would consist of 

 a critical discussion of the comparative systematic value of their different organs. I 

 purpose choosing this latter mode, for the following reasons. Firstly, because it ensures the 

 avoidance of superfluous repetitions, the existing arrangements of the Keratosa being con- 



(ZOOL. OHALL. EXP. — PART XXXI. — 1884.) Hh 1 



