240 PKOr. H. A. NICHOLSON AND DR. J. MTJRIE ON THE 



the horizontal laminse always porous nor the vertical pillars usually 

 tubular, as some have asserted. In one peculiar aberrant form, 

 Cauno;pora, there are, in addition, large, thick-walled tubes pene- 

 trating the mass vertically, and undoubtedly belonging to the 

 organism itself. In some forms, notably the genus Stromato- 

 cerium, there is a system of more or less perpendicular canals 

 and lacunae without walls ; in others there is a paucity or even 

 absence of such, though, in most, smaller and larger apertures 

 open superficially. A further system of stellate obliquely disposed 

 canals exists, in many forms, both deeply and on the surface of 

 the outer layers. While the tj^pical ^tromatoporcB are charac- 

 terized by horizontal laminae, supported by short upright pillars 

 enclosing cuboid chambers or cells, some take on a vesicular 

 character {ClatlirodiGtijon),^Xi^ others {PacJiy stroma) are destitute 

 of pillars. Still other examples, essentially Stromatoporoid in 

 aspect &c., assume a more indefinite minute structure, with a 

 tendency to a reticulate or trabecular formation. In certain 

 forms (notably Stylodictyon) a columnar character obtains, the 

 chambers showing a concentric arrangement round a dense but 

 reticulate centre. Thus by their intimate structural peculiarities 

 we attempt a tentative classification, wherein we can distinguish 

 at least seven types of construction which we rank provisionally 

 as genera, and we describe en passant a few new and remarkable 

 species. 



In discussing the affinities of Stromatopora and its allies, we 

 bring forward such evidence and argument as we believe is suffi- 

 cient to warrant our excluding them in the meanwhile from alliance 

 with the Nullipores, the Eoraminifera, the Hexactinellid Sponges, 

 the Polyzoa, the Corals, and certain fossil forms of uncertain 

 affinities. As respects their Hydrozoal connexion we express 

 ourselves with greater reticence, inasmuch as both in Hydractinia 

 and Millepora not only are there certain superficial resemblances 

 of considerable importance, but through the curious divergent 

 form Caunopora structural peculiarities present themselves which 

 possibly point to Hydrozoal relationships. Moreover, Mr. Carter's 

 late very shrewd observations among the chitinous and calcareous 

 TlydractinicB necessarily render the subject at issue open to 

 further research before the decided negative can be affirmed. 

 Mr. Moseley's * able investigations on the Hydrocorallincd 

 during the ' Challenger ' Expedition, while they yield valuable 

 ^ Philos. Trans. 1876, vol. clsvi. pp. 91-129, pis. 8 & 9. 



