INTRODUCTION. 



In the " Abhandlungen der Kngl. Preussichen Akademie der Wissen- 

 schaften" for 1894, 1895, and 1900 I have pubUshed three memoirs on the 

 Hexactinellida collected by the "Investigator" in 1885-1898 and placed at my 

 disposal by Prof. J. Wood-Mason and Dr. A. Alcock. 



At the latter's request I have now prepared a report embodying the results 

 pubhshed in those memoirs for an English translation. Making use of the 

 facts concerning these sponges since brought to light, through my investi- 

 gation of the Hexactinellida collected for the most part under the supervision 

 of A. Agassiz by the "Albatross" and through other investigations, I have 

 now re-examined the " Investigator " material. This report is therefore not a 

 mere translation of the German memoirs named above but a revised second 

 edition of their re-arranged contents. 



For the sake of completeness I shall first give a list of the Hexactinellida 

 collected in the Indian Ocean by other expeditions than those of the " Investi- 

 gator." 



I limit the Indian Ocean as follows -.—Pfesi ; Africa from Suez to Cape 

 Agulhas, and from thence to the South Polar circle, the meridian 20' B. 

 South: South Polar circle from 20= E. to 146° 50' 39" E. East : from the 

 South Polar circle to Tasmania, the meridian 146' 50' 39" B., then Tasmania, 

 Australia, the Sunda Islands and the East Indies. North : Asia from the Malayan 

 Peninsula to Suez. 



Before the "Challenger" Expedition only four species of HexactinelHda 

 were known from the Indian Ocean, namely : — 



(1) Eupledella cucumer R. Owen 1857, in Trajis. Linn. Soc, Yol. XXII, 

 (2), pp. 117-124, pi. XXI. Seychelles. 



(2) Gorbitella corbicula Bowerbank 1867, in Proc. Zool. Soc, London, 

 1867, p. 858. Isle de Bourbon. 



(3) Farrea occa Bowerbank 1862, in Phil. Trans., Vol. CLII, p. 747, pi. 

 XXXIII, f. 7. Seychelles. 



