382 On the Affinities of Astrosclera willeyana, Lister. 



&c* Aulena crassa (Carter) , with its main skeletal construc- 

 tion almost identical with that of Astrosclera, selects minute 

 particles of siliceous or quartz sand. Astrosclera selects the 

 more tractable spherules of an aragonitic sand. An artificial 

 aragonitic sand made after Meigen's recipe (Bericht nat. Gesell. 

 Freiburg, xiii. p. 9) resembles the supposed scleres of Astro- 

 sclera. Little masses of these spherules, each one of which 

 is a radiating aggregate, make not a bad imitation of fragments 

 of Astrosclera skeleton, for the artificial spherules vary in 

 size and becomo polyhedral with mutual pressure. 



The primarily separate spherules would gradually amalga- 

 mate to form walls, which would permit of the choanosome 

 growing into folds; the lumen of the latter would gradually 

 contract owing to the encroaching laminae. The vertical 

 acanthostyles in the tubular folds would tend to assume more 

 and more an oblique position. The thin sponge crust became 

 a disk, and the disk a column. 



The character of forming a skeleton of aragonite has 

 evidently been an eminently successful one for the little 

 IJymerhophia-Wke sponge, for examples have been recorded 

 from widely distant localities, viz. from 10 to 20 degrees 

 south of the Equator and from longitudes 105° E., 166° E., 

 and 175° W., trom depths of 35-100 fathoms on coral rock. 

 But apparently there have been penalties and drawbacks 

 associated with this strange success, for the sponge has 

 become subject to the attacks of boring organisms. 



The tubular and honeycomb style of architecture is not 

 uncommon among the Ectyonine relatives of Astrosclera. 

 Aulena (Holopsamvia) crassa (Carter), for instance, presents 

 a very similar appearance to Astrosclera both on the surface 

 and in section (see Lendenfeld, ' Mon. Horny Sponges/ 

 pi. viii. figs. 1, 2) ; here the echinating styles are smooth. 



I shall not attempt to give an account of the histology and 

 cytology of Astrosclera at present, because the specimens, 

 precious though they be, are not sufficiently well preserved. 

 1 shall be dredging off Christmas Island this autumn, and 

 if I am fortunate enough to procure more specimens of this 

 wonderful sponge I shall fix them at the moment of capture 

 and in accordance with the best methods. 



In the true siliGeo-calcareous sponge Merlia normani 

 (' Annals,' Feb. 1910, p. 288) the skeleton of calcite, which 

 is formed by an epithelium on the external surface, partly 

 supports the sponge, but chiefly shelters masses of archaeo- 



* For lists of calcitic and aragonitic organisms see Meigen, Centralb. 

 fur Mineralogy, 1901, p. 577, and Ber. nat, Gesellsch. Freiburg i. B. 1903, 

 xiii. p. 51. 



