238 On some new or {mperfectlij- known Stromatoporoids. 



latter. The general structure of the skeleton is also verj 

 similar to that of S. eifeliensis^ and the skeleton-fibre is tra- 

 versed by the same delicate, branching, microscopic tubuli. 

 S. arachnoidea has, however, the unique feature that the 

 entire space intercepted between the successive laminae (as 

 also the astrorhizal canals) is crossed by a system of curved 

 tabula3, which gives to the interlaminar spaces a characteristic 

 vesicular ajDpearance. In many sections of 8. eifeh'ensis we 

 can detect curved calcareous partitions which are apparently 

 of the same nature as those just alluded to ; but they are 

 always few in number and are often not recognizable at all. 

 For the present, therefore, I think we must regard the pre- 

 sent species as distinct. 



Formation and Locality. Rare, in the Middle Devonian of 

 Biichel (Paffrath district) ; and at Gees, in the Eifel. 



EXPLANATION OF THE PLATES, 



Plate VI. 



Fig. 1. Tangential section of Actinostroma dathratum, Nich. { = Stroma- 



topora conceyitrica, Barg.), enlarged about twelve times. Middle 



Devonian, Hebborn. 

 Fifj. 2. Vertical section of the same, similarly enlarged. 

 Fig. 3. Tangential section of Actinostroma clathratmn, Middle Devonian, 



Dartington, similarly enlarged. 

 Fig. 4. Tangential section of Actinostroma bifariuin, Nich., enlarged 



about twelve times. Middle Devonian, Biicbel. 

 Fig. 5. Vertical section of the same, similarly enlarged. 

 Fig. 6, Tangentiiil section of Actinostroma ? astroiteSj Rosen, enlai'ged 



about twelve times, Silurian, Oesel, 

 Fig. 7, Vertical section of the same, similarly enlarged. 

 Figs. 6 a, 7 a. Portions of the same sections, enlarged about twenty-four 



times. 

 Fig. 8. Tangential section of Actinostroma steJlulafum, Nich., enlarged 



about twelve times. Middle Devonian, Gerolstein. 

 Fig. 9. Vertical section of the same, similarly enlarged. 



Plate VII, 



Fig. 1. Tangential section of Actinostroma Schmidtii, Rosen, enlarged 



about twelve times. The section traverses part of an astrorhiza. 



Silurian, Oesel, 

 Fig. 2. Vertical section of the same, similarly enlarged. The section 



cuts one of the vertical ciinals (a) of the astrorhizal system. 

 Fig. 3. Tansrential section of Actiiwstroma intertextum, Nich., enlarged 



about twelve times. Wenlock Limestone, Iroubridge. 

 Fig. 4. Vertical section of the same, similarly enlarged. 

 Fig. 5. Tangential section of A. intertextum, xnx. suevicum, enlarged about 



twelve times. Silurian, Esthonia. 

 Fig. G. Vertical section of the same, similarly enlai'ged. 



