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



spicules placed in horizontal, transverse, and oblique directions, often crossing each other, 

 forming a more or less irregular network, and often closed at the top by a netted lid 

 formed of shorter spicules ; the base with elongated free spicules terminating in three or 

 four short spines, by which it is fixed to the mud. The sarcode mucilaginous, studded 

 with differently shaped spines, some of which are many rayed, stellate, with clavate 

 arms." 



In the system wliich Carter proposed ' in 1873 for the Hexactinellida he did not class 

 together the well-known forms hitherto united in the family of the Euplectellidse, but 

 referred Euplectella aspergillum to one of his three chief divisions, where the " spicules" 

 were "held together by silicified fibre "; the genus Habi'odictymi, Wyville Thomson, he 

 relegated to the groujD whose " spicules " were "held together by amorphous sarcode"; 

 while for Owen's Euplectella cuciimer, whose spicules are only united in the lower portion 

 of the sponge by being cemented with siliceous matter into a rigid framework, while they 

 remain isolated above, he instituted, because of this character, a special third division. 



As characteristic of Euplectella aspergillum, he noted that the body was " tubular, 

 unbranched, and closed at the extremity." This specific character, however, applies 

 equally well to Euplectella cuciimer, Owen, and to Habrodictyon, "Wyville Thomson. 

 The two species of the latter, Habrodictyon sp>eciosum and Hcdirodictyon corbicula, 

 although separated by Wyville Thomson, Carter thought it necessary to unite in one 

 species, Habrodictyon or Alcyoncellum speciosum. 



In 1874, Higgin ^ described the skeletal structure of a specimen of Euplectella 

 aspergillum preserved in the Liverpool Free Museum, which had already, on an earlier 

 occasion, been inspected by Wyville Thomson during his stay in Liverpool, and was 

 referred to in a letter from the Challenger in Good Words, July 1873, p. 510. That 

 communication by Wyville Thomson ran as follows: — "Several samples of Euplectella 

 very closely allied to the Philipjiine species, if not identical with it, came up in the trawl 

 off Cape St. Vincent, and gave us an opportunity for the first time of seeing this Sponge 

 alive. Dr. J. E. Gray writes to the Annals and Magazine of Natural History that 

 specimens have been received of Euplectella aspergillum in spirit, and that in these the 

 glassy framework is entirely masked by a soft browni corky coating of sarcode. Our fresh 

 specimens entirely bear out Dr. Gray's description. It would be diflicult to imagine that 

 the thick, somewhat clumsy, brown tube, perforated with irregular openings, contained 

 any arrangement of support so delicate and symmetrical." 



" Although the forms of all the spicules, down to the most minute and complicated, 

 are identical, the wall of the tube in the European specimens of Euplectella is not 

 coherent as in most of the Philippine examples. The original spicules of the skeleton 

 remain separate from one another, and do not become soldered together. One would 

 think that this would be at all events a perfect specific distinction, but one or two of the 



1 Ann. and Mag. Nat. Hist., ser. 4, vol. xii. p. 349. ■ Ann. and Mag. Nat. Hist., ser. 4, vul. xiii. pp. 44-48. 



