THE ANATOMY OF THE MADREPORAEIA. 261 



Fig. 14. — Transverse section of half of the calyx of Rhodopsamniia, 

 along the plane a, Fig. 13 (camera drawing). The 

 numerals 1. 2, 3 are placed in the entocoeles formed by a 

 pair of mesenteries of those orders. Complete systems, 

 1, 3, 2, 3, 1, are only found in the region of the directives. 

 The dashed numerals, 1', 2', 3', are placed in the external 

 chambers which correspond to the entocoeles. ext.h.iv. 

 External body-wall. Corallum deep black, soft tissues in 

 lighter black lines. 



Fig. 15. — Similar section along the plane 6., Fig. 13. The septa have 

 fused into the columella, and are numbered 1, 2, 3, 

 according to their orders. /. Cavity filled with sponge 

 spicules, g. Line of tissue which may belong to the polyp. 



Fig. 16. — Mesenterial filament of Rhodopsammia in transverse section. 



Fig. 17. — Part of Fig. 14, enlarged to show the relations of the 

 three body4ayers. Mesoderm black, corallum grey. c. 

 Thecal canal system in transverse section, c'. External 

 chambers, corresponding to exocoeles and entocoeles, in 

 each of which lies a costa. 



Fig. 18. — Part of the thecal canal system of Rhodopsammia, after 

 removal of the corallum by decalcification. 



Figs. 19, 20, and 21. — Diagrams of the relations of a complete system 

 of septa of Rhodopsammia at different heights. The 

 numerals are placed at the bases of the entosepta. 



Fig. 22. — Calyx of Rhodopsammia, viewed from above. From a 

 specimen in the British Museum. 



