GENUS ACTINOSTROMA. 75 



V. FAMILIES AND GENERA OF THE STROMATOPOROIDS. 



Fam. 1. Actinostromioe, Nich. 



Skeleton composed of distinct " radial pillars," which give rise to concentrically 

 disposed "laminae," by the production at successive levels of horizontal processes 

 or " arms," which inosculate to form a " rectilinear " meshwork. 



In this family I include those Stromatoporoids in which the coenosteum is 

 clearly composed of radial pillars and concentric laminae, the latter formed by the 

 anastomosis of radiating calcareous fibres, in such a manner as to give rise to a 

 loose network, the meshes of which are typically angular. The skeleton is not a 

 continuously reticulated one, and therefore in this family, unlike what occurs in the 

 Stromatoporidce, the radial pillars are always recognisable in tangential sections as 

 distinct from the horizontal processes to which they give rise. The skeleton-fibre 

 is not minutely porous, and the radial pillars are often hollow internally. Definite 

 zooidal tubes, as distinct from the angular meshes formed by the inosculating 

 horizontal processes, are not present. The surface is granulated or tuberculated 

 by the projecting upper ends of the radial pillars. Astrorhizae may be present or 

 absent. The form of the coenosteum is exceedingly variable, an epitheca being 

 sometimes present, sometimes absent. 



Genus Actinostroma, Gen. ?wv. 



(= Stromatopora, auctt.). 



Radial pillars " continuous," i.e. passing continuously through a number of 

 laminae and interlaminar spaces. When the laminae are grouped into " latilaminae,'' 

 as is not uncommonly the case, the radial pillars are continued from the under 

 surface of each latilamina to the upper surface. The horizontal processes or 

 " arms " are delicate, solid or hollow fibres, which are given off from the radial 

 pillars in whorls, at corresponding levels, and which unite to form an angular 

 meshwork. Astrorhizae may be present or absent. 



Owing to the discovery that the original specimen of Stromatopora concentrica, 

 Goldf., possesses a continuously reticulate skeleton of the " Milleporoid " type, I 

 have been compelled to propose the new generic name of Actinostroma for those 

 widely-spread Stromatoporoids which had up till now been generally regarded as 

 referable to the genus Stromatopora, Goldf. The species, which has been generally 



