60 BRITISH STROMATOPOROIDS. 



in specimens of Idio stroma and of Stachyodes verticillata, M'Coy (Plate VIII, fig. 

 12). The form, however, which displays this membrane most completely is the 

 singular Amphipora ramosa, Phill. (Plate IX, fig. 1), in which many examples have 

 the surface entirely covered with an apparently imperforate calcareous envelope. 

 In this case, however, it can be shown, that underneath this membrane, between it 

 and the true surface, are developed numerous comparatively large-sized lenticular 

 vesicles. I am disposed to regard these marginal vesicles as corresponding to the 

 " ampullae " which have been shown by Professor Moseley to contain the gono- 

 phores in the recent Stylasterids. If this view be accepted, it seems probable that 

 the development of the calcareous pellicle above alluded to, in all those Stromato- 

 poroids in which it occurs, is connected with the formation of the reproductive 

 zooids. I shall, however, have occasion to refer to this point again. 



In all the species of Actinostroma, such as A. clathratum, the surface (Plate II, 

 fig. 11) is studded, in well-preserved examples, with numerous minute projecting 

 tubercles, which are simply the upper ends of the radial pillars, and represent the 

 small spines in Eydractinia. I have never succeeded in detecting any apertures in 

 these tubercles, but it is possible that such exist. 



In the nearly allied genus Clathrodictyon, Nich. and Mur., either the surface is 

 covered with tubercles similar to those of Actinostroma (Plate II, fig. 12), or the 

 tubercles have coalesced with one another to form vermiculate ridges (Plate II, 

 fig. 13). 



In the genus Labechia, E. and H., the upper ends of the radial pillars project 

 above the surface as prominent tubercles (Plate III, fig. 12), much in the same way 

 as in Actinostroma,, except that, owing to the stoutness of the pillars, the tubercles 

 are much more pronounced. The tubercles may be quite separate, or they may be 

 partially confluent, so as to form sinuous rows (Plate III, fig. 13), these variations 

 occurring in individuals of the same species (e.g. L. conferta, Lonsd.). In some 

 species, however, as in L. serotina, n. sp. (Fig. 4), and L. alveolaris, n. sp., the 

 tubercles coalesce so as to form a sort of labyrinthine pattern, after the fashion of 

 the corallites in the genus Halysites. Whether the tubercles in Labechia are 

 perforated or solid, is a point very difficult to determine positively. In some forms, 

 such as L. seroti?ia, they certainly would seem to be solid. In others, such as L. 

 conferta, Lonsd., they sometimes have all the appearance of being solid, while at 

 other times they show distinct round pits at their summits (Plate III, fig. 14) ; 

 but it is quite possible that this latter phenomenon may be simply the result of 

 weathering. 



In a large number of Stromatoporoids the surface normally shows larger or 

 smaller conical eminences, which may be distinguished from the granules and 

 tubercles formed by the upper ends of the radial pillars under the name of 

 " mamelons " or " monticules " (the " Warzen " and " Hocker " of German writers). 



