HICKSON— POLYTREMA 461 



EXPLANATION OF THE PLATES. 



Plate 30. 



Fig. 1. Polytrema miniaceum. A specimen from 90 metres off Ki Islands x 4£ diameters, showing the 



characteristic pale pink (or apricot red) colour. 

 Fig. 2. Homotrema rubrum from Providence 50 — 78 fathoms x 4£ diameters, showing a darker (salmon 



colour) red tint. 



Fig. 3. Sporadotrema cylindricum, fac. Providential; from Providence 70 fathoms x 2 diameters, showing 

 the characteristic orange yellow colour. 



Fig. 4. Sporadotrema cylindricum, fac. Saya de Malhensis. Saya de Malha 29 fathoms x 2 diameters 

 showing the pale pink colour. 



Fig. 5. Sporadotrema mesentericum from Torres Straits x 2 diameters, showing the characteristic dark 



red colour. 

 Fig. 6. Sporadotrema cylindricum, fac. Amirantise. Amirante 34 fathoms x 2 diameters, showing a 



darker red colour than (in Fig. 4) fac. Saya de Malhensis. 

 Fig. 7. Sporadotrema cylindricum, fac. Amirantias. Saya de Malha 26 fathoms xl| diameters. This is 



an orange coloured variety of the facies. 



Plate 31. 



Fig. 8. Polytrema miniaceum. A specimen from 90 metres off Ki Islands (Siboga Expedition) x 4^ 

 diameters, showing the branching method of growth. 



Fig. 9. Homotrema rubrum from Providence 50 — 78 fathoms x 4£ diameters, showing the characteristic 



solid and tuberculate method of growth. 

 Fig. 10. Sporadotrema cylindricum, fac. Providentiae; from Providence 70 fathoms x 2 diameters. Note 



that the magnification of this is much less than that of Figs. 8 and 9. 



Fig. 11. Sporadotrema mesentericum (Carter) from Torres Straits (Haddon coll.) x 2 diameters. 

 Fig. 12. Sporadotrema mesentericum from Torres Straits x 2 diameters. Side view showing the convex 

 surfaces marking the outlines of the chambers. 



Fig. 13. Sporadotrema cylindricum, fac. Saya de Malheusis. Saya de Malha 29 fathom-; x 2 dia meters. 

 Fig. 14. Transverse section through a stem of Sporadotrema cylindricum, fac. Providentiae x 5 dia meters, 



showing the thick outer wall perforated by the foramina, and the ring of chambers surrou nding a 



more solid core. PL 32, fig. 20. 

 Fig. 15. Sporadotrema cylindricum, fac. Saya de Malhensis. A terminal branch x 9 diamete rs. To 



show the outlines of the chambers clearly marked at the extremity where they are superimposed, 



becoming less clearly marked as the walls thickened and quite obliterated at the base of the branches 



and below. 

 Fig. 16. Sporadotrema cylindricum. View of the same specimen as in fig. 15, to show the free edge. 



The spout-like openings of the terminal chambers may be seen and also the scaffolding of spicules 



which support the growth of the terminal chambers. 

 Fig. 17. Vertical section through Polytrema cylindricum, fac. Providentiae x 6 J diameters, showing the 



arrangement of the chambers in the stem and in one of the branches. 



Plate 32. 



Fig. 18. Transverse section of a thick branch of a Polytrema, showing four concentric circles of chambers. 



x 100 diameters, p. pillar pores. 

 Fig. 19. Transverse section of one of the verrucose processes of a Homotrema, showing that the outer 



wall (0) of the outer circle of chambers alone are foraminate. The other chambers composing the 



process are not arranged in definite circles, have imperforate walls but communicate with one another 



by large open passages, x 100 diameters. 



SECOND SERIES— ZOOLOGY, VOL. XIV. 59 



