2 9 



We have seen above that 5". decumbens is identical with 5". bistellata and that specimens 

 1031, 1455 a-c, 1945 from the Siboga collection belong to the same species. We saw Iikewise 

 that through B.M. 38 the specimens 1402 and 1421 are jnst as vvell forms of trop. tegens. 

 Hut the latter two show incipient papillae, by which they form transitions to trop. pyramidalis 

 or trop. digiiata. Consequently the species of trop. tegens can not be separated from those of 

 trop. pyramidalis or trop. digitata. Moreover we have in 1480 a form which might be placed 

 within tegens just as well as within pyramidalis-, to the former it is related by its spinispirae, 

 to the latter by its processes. Specimens 410 and 300 on the other side show nearer relation 

 to tegens, possessing hardly any processes and more resembling thick cushion-shaped specimens 

 of this tropus, whereas they entirely miss the robust spinispirae and in this respect are closer 

 related to trop. pyramidalis. If we do so the pyramidal shape of this tropus is no more constant 

 Indeed all is fluctuating. 



Between trop. digitata and trop. pyramidalis there are numerous transitions; 410 and 

 1092 resemble each other strikingly, but in 410 some spinispirae are larger and formed like 

 those of 426 a-c (PI. IX, lig. 3), whereas 1092 only possesses small ones. Typical forms of 

 trop. pyramidalis possess, in addition to the ordinary small spinispirae, others which are slightly 

 thicker or longer (PI. XII, fig. 3); in this respect 1403 ought do be considered as trop. pyra- 

 midalis^ the spinispirae exactly resembling those of S. wilsoni B. M. 15- Kut they resemble at 

 the same time those of 5. vagabunda B.M. 24 (Pb XI, fig. 7). Externally 1403 and 1075, from 

 the same locality, resemble each other very much; their spinispirae show slight differences, the 

 latter are more like those of B. M. 24. It is certainly impossible to separate as different species : 

 wilsoni B. M 15, vagabunda B. M. 24, 1403 and 1075- 



Specimen 1947 has the external appearance of Suberites inconstans var. digitata (B. M. 11) ; 

 with regard to the tylostyles they agree; but in the former abundantly I fin cl small spinispirae, 

 in the latter none. Specimen 1949, from the very same locality as 1947, possesses still lower 

 processes than the latter. It has, as we have seen, large portions on the surface which correspond 

 to S. areolata B.M. 2; moreover we find spinispirae which are like those of 426 a-c The sponge 

 in some respects ought to be considered as trop. tubulifera, in others as trop. pyramidalis. 

 Specimen 1988 shows similar spinispirae (PI. IX, fig. 8) and in external appearance it connects 

 again 1949 with trop. pyramidalis. Such specimens like 1947, 1949 and B. M. 11 clearly show 

 that the two tropi are not specifically different. 



Ridley has already stated that Spirastrella vagabunda is closely allied to Hymeniacidon 

 angulata Bwk. We have seen above that on the other side the latter is indeed identical with 

 Suberites inconstans Dy. Dendy showed how variable this sponge is and we need not further 

 discuss the specific identity of trop. concrescens, glaebosa and tubulifera. Summa summarum we 

 arrive at the conclusion that all the above mentioned specimens and "species" belong to one 

 single, exceedingly variable species Spirastrella purpurea. We may distinguish certain groups 

 of specimens formed by the same tropus; to such a tropus belongs a number of specimens 

 typically, others are again somewhat modified and form transitions to other tropi. These may 

 be characterised as follows : 



