20 BRITISH STROMATOPOROIDS. 



In 1880, an important memoir was published by Prof. Ferd. Roemer on the 

 genus Caunopora, Phill. (' Geological Magazine,' dec. ii, vol. vii, p. 343). 

 As previously mentioned, tliis veteran palaeontologist, as long ago as 1844, 

 expressed tlie opinion that Caunopora placenta, Phill., was founded upon specimens 

 of Stromatopora concentrica, which had "surrounded and overgrown the stems of 

 Syringopora" In the present memoir, Roemer states that the tubes of Caunopora 

 are not, strictly speaking, referable to Syringopora, but rather belong to Aulopora, 

 especially to A. repens. He regards Caunopora placenta, Lonsd. sp., as being, 

 therefore, the result of the combined growth of a colony of Stromatopora with 

 one of Aulopora ; the latter extending its tubes upwards, as the former adds new 

 layers to its surface, and thus preventing itself from being entirely covered up and 

 killed. The occurrence of thick masses of Caunopora is accounted for on the 

 hypothesis that " the vertical tubes do not necessarily all belong to the same indi- 

 vidual of Aulopora, but different colonies of these little creeping Corals attached 

 themselves repeatedly to the surface of succeeding concentric layers of Stromatopora, 

 and were covered by the succeeding one." He adds further that " in fact, on vertical 

 sections of Caunopora the same vertical tubes can never be followed up through the 

 whole mass, but they are mostly only a few lines in length." On this point, however, 

 I am unable to agree with Prof. Roemer. Even in very thick specimens of Cauno- 

 pora, the same tubes may often be traced continuously for long distances, and in 

 laminar specimens, an inch or more in thickness, most, if not all, of the tubes pass 

 directly from the top to the bottom. Roemer, moreover, states that a Silurian 

 Stromatoporoid (which he considers to be S. striatella) also occasionally exhibits 

 the structure of Caunopora, the tubes in this case also being produced by a species 

 of Aulopora. Specimens of this nature, in the author's view, had been previously 

 described from the Drift of Groningen, in Holland, being named Syringopora fili- 

 formis by Goldfuss (' Petref . Germ.' Taf. xxxviii, fig. 15), and referred by Roemer 

 himself to Eeliolites inter stincta (' Diluvial Geschiebe von Sadewitz,' t. iv, fig. 2 c). 

 As regards, finally, the perforated tubercles or eminences which are found on the 

 surface of various Stromatoporoids, Prof. Roemer brings forward an ingenious 

 explanation; namely, he discovered that underneath such openings were some- 

 times to be found the tubes of species of Sjrirorbis, and he therefore suggests that 

 " the hole on the top of the tubercle is the opening of the canal by which that 

 little animal kept up its communication with the surrounding water, and the 

 tubercle was formed by the bending upwards of the successive layers of Stromato- 

 pora round the canal." That buried specimens of S2rirorbis may thus give rise to 

 superficial openings, simulating " oscula," is a point which I can myself confirm, 

 from observations upon various of the Silurian Stromatoporoids. Moreover, suc- 

 cessive generations of Spirorhes may in this way become embedded in the skeleton 

 of a Stromatoporoid, and they often assume a rough grouping in vertical lines. 



