62 BRITISH STROMATOPOROIDS. 



of the genus Aciinostroma (such as A. clathmtum), it is often possible to recognise 

 the angular meshes formed by the inosculating horizontal " arms " given out by the 

 radial pillars, and we have seen that these meshes in all probability represent the 

 zooidal apertures. 



On the other hand, in all the typical species of the genus Stromatopora, Goldf., 

 well-preserved examples exhibit the rounded, oval, or vermiculate apertures of the 

 zooidal tubes. In many of such forms, therefore, the general aspect of the surface 

 is exceedingly like that of an Alveolites or Pachypora, except that the zooidal 

 openings are mostly smaller than they are in the Corals just alluded to. Precisely 

 similar apertures are seen on the surface of the species of Idiostroma (PL IX, fig. 

 9), Stachyodes, Barg. (PL VIII, fig. 12), and certain examples of AmpMpora 

 ramosa, PhilL, sp. In the genus Stromatoporella, the surface in well-preserved 

 examples exhibits rounded tubercles, which are perforated at their summits by round 

 apertures which can hardly be anything else than the openings of the zooidal tubes. 

 These are well seen in specimens of Stromatoporella granulata, Nich. (PL I, fig. 

 14), and 8. (Diapora) laminata, Barg. (PL X, fig. 4). 



The conspicuous round apertures which are seen on the surface of specimens of 

 Gaunopora, PhilL, cannot be considered apart from the question of the walled 

 tubes to which they belong — a question which will be fully dealt with at a later 

 period. 



Lastly, the surface of many Stromatoporoids exhibits the astrorhizas and their 

 canals. These, when present, vary much in size, but it is unnecessary to say more 

 about their characters here. As has been already seen, they are often apparently 

 entirely absent in certain species, even when present in closely allied types. This, 

 however, cannot be considered as surprising, when it is remembered that the corre- 

 sponding coenosarcal canals of Hydractinia, though so characteristic of many 

 species, are said to be wanting in certain forms of the genus. 



(lc) The Reproductive Organs. — As regards most of the Stromatoporoids, the 

 process of reproduction is wholly unknown. Accepting, however, the relationship 

 of the Stromatoporoids to the Hydrocorallince, it would be naturally expected that 

 the reproductive zooids should have been lodged in special cavities within the 

 skeleton, such as have been described by Professor Moseley in the case of the 

 Stylasteridce, under the name of "ampullar." As a matter of fact, structures 

 which do appear to be of the nature of " ampullae," are to be recognised in certain 

 of the Stromatoporoids. Thus, as has already been alluded to, many examples of 

 AmpMpora ramosa, PhilL, possess a series of large-sized lenticular vesicles, which 

 form a sort of marginal zone to the cylindrical ccenosteum, and which are covered 

 over by a thin calcareous membrane (PL IX, figs. 2 and 3). Many examples of this 

 species are, however, wholly destitute of these " marginal vesicles " and of the 

 membrane which encloses these (PL IX, fig. 4). From their form and position, as 



