{mperfcctly-hnoion Species of Stromatoporoids. 9 



tlian a centimetre in height, in which case tliey are compara- 

 tively few in number. More usually they are smaller, per- 

 haps 2 or 3 millim. in height, and in this case they are 

 numerous. When well developed each of these pointed 

 eminences consists of concentrically laminated tissue traversed 

 centrally by the axial canal of an astrorhizal system, and 

 having the external opening of the same at its apex, while 

 the astrorhizal twigs run down its sides externally. 



The surface presents curious and very puzzling variations 

 in different examples, or in different regions of the same 

 specimen. Sometimes the whole, or a part only, of the 

 surface is covered with minute rounded or elongated tuber- 

 cles, which sometimes coalesce into vermiculate ridges, and 

 which may have their apices perforated with minute circular 

 apertures. This seems to be the normal condition of the 

 surface. In many specimens, however, this granulated sur- 

 face is extensively, or completely, concealed from view by the 

 development of a delicate smooth calcareous pellicle or mem- 

 brane. This external membrane may pass unbrokenly over 

 the mamelons as well as over the general surface ; but com- 

 monly the apices of the mamelons show a few small apertures 

 or the single larger opening of an astrorhizal canal. In this 

 latter case the appearances presented remind one of the general 

 surface of Distichopora at points where ampullge are de- 

 veloped. 



As regards internal structure, the general appearances pre- 

 sented by tangential and vertical sections (PI. I. figs. 2 and 3) 

 are very similar to those of corresponding sections of Stromato- 

 porella eifeliensis, Nich., and need not be more minutely dis- 

 cussed here. The present species is distinguished from S. 

 eifeliensis, as from the other related species of Stromatopjorellaj 

 by its uniformly encrusting habit, the development of pointed 

 mamelons, and the characters of its surface. It does not 

 appear to differ, to any marked extent, from an encrusting 

 Stromatoporoid from theHamilton formation of North America, 

 to which I gave the name of Stromatopora nulliporoides [loc. 

 cit. supra) ; and the latter name will therefore probably have 

 to be regarded as a synonym. It also seems to me very 

 probable that the form described by Professors Hall and 

 Whitfield, from the Chemung group of North America, under 

 the name of Coenostroma incrustans [loc. cit. supi'o) will prove 

 to be really identical with the present species. 



Formation and Locality. Common in the Middle Devonian 

 formation of Biichel (in the PafFrath district) . I have also 

 found it at Paffrath, and, more rarely, at Gerolsteiu and 

 Biircndorf (Hillesheim) in the Eifel. 



