likewise prefering calcareous matter, as Coralline Algae, (old) Corals etc. ; it does not bore 

 holes, but it insinuates itself in every fissure or gap, which happens to be formed on the surface. 

 If circumstances are favourable the three genera may grow beyond their substratum and reach 

 considerable sizes. In this respect Cliona the least, unless Raphyrus hixonii of Lendenfeld 

 (1886 p. 562) turns out to be a "free" Cliona. In this latter state the genus forms irregularly 

 spherical masses and never assumes a proper shape, nor processes of any length or characteristic 

 shape. Poterion on the contrary typically forms cups, showing a distinct difference on its outer 

 and inner wall : the incurrent apertures are on one side, the excurrent ones on the other ; a 

 very remarkable feature, to which Ridley & Dendy draw attention in their description of Cliona 

 dissimilis. Perhaps the most striking feature of Spirastrella lies in the marked tendency to 

 form digitate processes, which may entirely change the external appearance. Even if there were 

 no other characters I should consider these sufficiënt to keep the three genera separated. 



II. LIST OF SPECIES DESCRIBED AS BELONGING TO SPIRASTRELLA. 



(chronologically). 



1868 Spirastrella cunctatrix O. S. Cf. p. 9. 



1875 Spirastrella vidua O. S. p. 120. Since Thiele (1903 a pp. 393, 395) found that in 



addition to the spicula mentioned, acanthostyli occur, and that the " Walzensternen" 



are of a peculiar character, this species can no longer remain under Spirastrella. 

 1884 Spirastrella congenera Rdl. Cf. p. 12. 



1884 Spirastrella dectimbens Rdl. Cf. p. 12. 



1884 (a) Spirastrella pulvinata (Bwk.) Rdl. Cf. p. 11. 

 1884 Spirastrella punctulata Rdl. Cf. p. 14. 



1884 Spirastrella purpurea (Lmk.) Rdl. Cf. p. 8. 



1884 Spirastrella transitoria Rdl. Cf. p. 14. 



1S84 Spirastrella vagabnnda Rdl. Cf. p. 14. 



1886 Spirastrella massa Rdl. & Dy. Cf. p. 17. 



1886 Spirastrella' neocomiensis Hinde, p. 437. Fossil. 

 1886 Spirastrella papillosa Rdl. & Dy. Cf. p. 17. 



1886 Spirastrella solida Rdl. & Dy. Cf. p. 17. 



1888 Spirastrella australis Ldfd. p. 57. Description without any illustration. It is impossible 



to form an opinion about this sponge. 

 1890 (a) Spirastrella aculeata. Tops. p. 69; see also Tops. 1892 p. 217 and 1904 («) p. 114. 



The sponge possesses oxea in stead of styli or tylostyli. For this reason I provisionally 



do not admit it in the genus Spirastrella. 

 1894 Spirastrella coronaria Tops. p. 29. 



1S96 Spirastrella cylindrica Kieschn. Cf. p. 21. 



1896 Spirastrella dilatata Kieschn. p. 534; see also Thiele 1900 p. 70. Insufhciently 



described to form an opinion. 



