imperfectly -known Species of Stromatoporoids. 311 



The surface is undulating and is destitute of astrorhizal 

 eminences or " mamelons ; " but there are well-developed and 

 much-branched astrorhizge, the centres of which are placed 

 4-5 millim. apart. The astrorhizse are not vertically super- 

 imposed in groups. 



The skeleton-fibre is minutely porous and is incompletely 

 reticulated, the radial pillars to a large extent preserving 

 their distinctness. Hence in tangential sections (PL VIII. 

 figs. 9 and 11) the cut ends of the radial pillars are more or 

 less clearly recognizable as rounded or oval porous masses, 

 united by irregular and exceedingly delicate connecting- 

 processes. In vertical sections (PI. VIII. fig. 10) the radial 

 pillars are seen to be continuous from the top to the bottom 

 of each latilamina — except when cut obliquely — and the spaces 

 separating them are crossed by irregular transverse plates or 

 " tabula?," and represent the zooidal tubes. About five or six 

 pillars with their intervening tubes occupy the space of 2 

 millim. measured transversely. In tangential sections the 

 zooidal tubes appear as small rounded apertures in the skele- 

 tal network, and the branching astrorhizai are well displayed. 



Obs. Sttomatopora antiqua presents us with a type in many 

 respects intermediate between Stromatopora, Goldf. (as now 

 defined), and Syringostroma, Nich. Though agreeing in 

 general characters with the typical species of Stromatopora, the 

 present form shows a strong relationship with Syringostroma, 

 this being especially shown by the comparative distinctness of 

 the radial pillars as definite structures. In the former genus, 

 on the other hand, the vertical radial pillars are more or less 

 undistinguishably merged with the horizontal connecting- 

 processes, the skeleton thus becoming completely reticulate. 

 None of my specimens of S. antiqua are in a state of 

 thoroughly satisfactory preservation, and it is possible that 

 the examination of more perfect specimens might show that 

 the species is properly referable to Syringostroma, from the 

 known species of which it could be readily differentiated. In 

 the genus Stromatopora the present form presents most like- 

 ness to S. typica, K,os., from which it is separated by the 

 more complete preservation of the radial pillars, the less 

 perfect reticulation of the skeletal framework as seen in tan- 

 gential sections, and the more markedly latilaminar mode of 

 growth. 



Formation and Locality. Niagara Limestone, Thorold, 

 Ontario {coll. H. A. Nicholson). A poorly preserved speci- 

 men in dolomitic limestone of Niagara age from Durham, 

 Ontario {coll. Oeol. Survey of Canada), may also possibly 

 belong to this species. 



22* 



