GENUS STROMATOPORA. 91 



persistent in the interior of the reticulate skeleton-fibre. Many Stromatoporoids, 

 moreover, possess exceedingly well-developed astrorhizal canals, the structure 

 of which is entirely similar to that of the same structures in the Actinostromids. 



Genus Stromatopora, Gold/, (emend.) 



(' Petrefacta Germanise,' Bd. i, p. 21, 1826.) 



Coenosteum usually massive or laminar, and generally furnished with an epi- 

 theca. The skeleton is completely reticulate, the radial pillars and their connect- 

 ing-processes being so far fused together as to give rise to a trabecular or vermicu- 

 late tissue, traversed by irregular zooidal tubes. Concentric laminae are usually 

 very imperfectly developed. The growth is very commonly by " latilaminas," the 

 radial pillars being continued from the top to the bottom of each latilamina ; but it 

 is rare for the pillars to have any distinct existence as separate structures. The 

 zooidal tubes appear to be in general of one kind only, and they are traversed by 

 a larger or smaller number of transverse partitions or " tabula?." Astrorhizae are 

 usually largely developed. 



As previously explained, the genus Stromatopora, Goldf., has hitherto been 

 generally taken as including the forms which have been here placed in the genus 

 Actino stroma. I have, however, examined the original type-specimen of 8. concen- 

 trica, Goldf. (' Petref. Germ.,' Taf. VI, fig. 5), of which Prof. Schluter was so good as 

 to have thin sections prepared. I have also made a minute examination of a 

 number of examples which I collected in the Eifel myself, and which in all 

 respects agreed precisely with the type-specimen of S. concentrica, the type-species 

 of the genus Stromatopora, Goldf. The result of this has been to render it certain 

 that the genus Stromatopora, Goldf., comprises forms entirely distinct from those 

 which have usually been placed under this head. The genus is, in fact, the repre- 

 sentative of a large and very natural series of Stromatoporoids which abound in 

 the Silurian (Upper-Silurian) and Devonian formations. One well-marked example 

 of this genus was described by Dr. Murie and myself from the Niagara Limestone 

 of North America under the name of P achy stroma antiquum (' Journ. Linn. Soc.,' 

 vol. xiv, p. 223, 1878), and we made this the type of the new genus Pachystroma. 

 This genus must, however, be now regarded as a synonym of Stromatopora, G oldf. 

 Other types of the genus Stromatopora have been described by different authors 

 as belonging to the so-called " Caunopora" of Phillips; but I shall subsequently 

 show that whatever conclusion we may form as to the nature of " Caunopora" it 

 cannot be regarded as a genus of Stromatoporoids. 



The general texture of the skeleton in the genus Stromatopora, Goldf., is often 



