102 Proceedings of the Boy at Physical Society. 



between the larger polypes, in the nature of the septa, the 

 absence of a differentiated wall to the larger tubes, and the 

 apparent want of tabulae in the interstitial tubuli. 



X. HELiOPORiDiE. — This family has been constituted by 

 Mr Moseley (Phil. Trans., vol. clxvi., p. 92, 1876) for the 

 reception of the extraordinary Eecent Heliojiora and the ex- 

 tinct Heliolites and its allies. The corallum in this family is 

 composed of two sets of corallites, a larger and a smaller, the 

 latter hitherto improperly spoken of as " coenenchymal 

 tubuli." The larger tubes are furnished with delicate septa 

 (generally twelve in number), and are traversed by remote 

 tabulae. The smaller tubes everywhere surround the larger 

 ones, have no septa, and are crossed by close- set tabulae. 



Mr Moseley has shown that the polypes of Heliopora are 

 of the Alcyonarian type, with eight pinnately-fringed ten- 

 tacles and eight mesenteries. The septa, thus, do not cor- 

 respond with the mesenteries, and are, therefore, to be 

 regarded as "pseudo-septa." The small interstitial tubes 

 are occupied by rudimentary sexless zooids, without mouths, 

 but freely communicating with the body-cavities of the 

 sexual zooids by means of transverse canals. Heliopora itself 

 is Eecent, Tertiary, and Cretaceous ; Polytremacis is Cretace- 

 ous ; while Heliolites, Plasmopora, and Propora are Palaeozoic. 



XI. CH^TETiDiE. — This group is made up of very hetero- 

 geneous materials, and will undergo disintegration when sub- 

 jected to a sufficiently searching investigation. As it is even, 

 the lines along which this disintegration will take place are, 

 to some extent, discernible. Taking the group as it stands 

 at present, no other general definition of it seems possible 

 than that it comprises very variously -formed corals, composed 

 of contiguous, thin- walled, mostly prismatic corallites, which 

 have imperforate walls, are intersected by well-developed 

 tabulae, and are destitute of septal laminae or spines. 



The typical members of the group, such as Chxtetes radians, 

 Fischer, and its few immediate allies, possess coralla in all 

 essential respects similar to those of the Favositidm, except 

 that '' mural pores " or other openings in the walls are want- 

 ing, while there are (in reality) no trace of septa. These two 

 last-mentioned differences are, of course, sufficient to show 



