302 Structure and Affinities of Heliopora cserulea, #c. [June 21. 



Under the Autothecalia I class Tubipora, Syringopora, Syringolites, 

 the Favositidce, and, provisionally, the Colnmnariadce. 



Under the Cosnothecalia I class Heliopora, Heliolites, Thecia, 

 Plasmopora, Propora, Lyellia, the Chcetetidce, and, provisionally, 

 Tetradium, Halysites, and the Monticuliporidce. 



The genns Heliopora is not the only Alcyonarian with a distinct 

 ectodermic skeleton. I brought back with me from Diego Garcia 

 two small Alcyonarians of the genus Xenia. One of the species is 

 referable to Xenia umbellata, Savigny, var. ccerulea. The other I 

 am describing elsewhere as a new species, under the name Xenia 

 garcice. These forms both possess a discontinuous skeleton, formed 

 of the minute corpuscle-like spicules characteristic of the Xeniidse. 

 In X. umbellata, the spicules in the exsert moieties of the polyps are 

 wholly ectodermic, and none are found in the mesogloea. In the 

 stem the external ectoderm is filled with spicules, and the so-called 

 ccenenchyme proves to be nothing more than the fused ectoderm of 

 the basal moieties of the polyps, which is traversed by strands of 

 mesoglcea binding the polyps together, and by endodermic canals 

 which place the polyp cavities in communication with one another. 

 The mesoglcea of the basal moieties of the polyps, as well as the 

 connecting strands of mesoglcea, are quite free from spicules, which 

 are, however, abundant in the mass of fused ectoderm occupying the 

 spaces between the polyps. 



In Xenia garcice the spicules are, as in X. umbellata, ectodermic in 

 the exsert moieties of the polyps, and in the ectoderm covering the 

 stem. The basal moieties of the polyps are provided with a much 

 thicker mesoglcea, which is, however, free from spicules, except 

 where the mesogkeal laminae of adjacent polyps become fused, in 

 which case intrusive ectoderm cells and spicules are found in the 

 fused thickened areas. Elsewhere the basal portions of the polyps 

 are separated, as in X. umbellata, by ectoderm containing spicules, 

 the mass of which is much less abundant than in X. umbellata. 

 There is also in X . garcice a special system of superficial endodermic 

 canals, which lies immediately below the surface in the upper part of 

 the stem. 



I have further been able to examine some specimens of Heteroxenia 

 elizabethce, collected by the late Dr. Gulliver, at Zanzibar, and given 

 by him to the Linacre Department at Oxford. I am able to confirm 

 Kolliker's account of this genus, which exhibits a well-marked 

 dimorphism, the colony consisting of fertile autozooids surrounded by 

 more numerous sterile siphonozooids. The spicules of Heteroxenia 

 elizabethce resemble those of Xenia umbellata and garcice, in being 

 minute and entirely ectodermic in the exsert moieties of the polyps. 

 The stem, however, differs considerably from that of X. umbellata, 

 and is more specialised than that of X. garcice. Instead of the 





