ZOOIDAL TUBES. 51 



Stromatopora (viz. S. Bupschii, Barg., and S. biicheliensis, Barg.), which occur in 

 the Devonian formation of both Britain and Germany, and in which these partitions 

 in the zooidal tubes are very well shown (Fig. 6). Nor do I see, for my own part, 

 any reason for doubting that these transverse partitions in the zooidal tubes agreed 

 in function, as they undoubtedly do in structure and position, with the "tabulae" 

 in the tubes of Millepora. If this be admitted, we have in the genus Stromatopora, 

 Goldf . — and I am not aware that this fact has been previously clearly demonstrated 

 — a group of Stromatoporoids in which the skeleton was provided with distinct 

 tabulate tubes in which the individual zooids were contained. 



Moreover, with the recognition of this fact it becomes comparatively easy to 

 demonstrate the existence of similar zooidal tubes in other Stromatoporoids, in 

 which they occur in a more imperfect and less completely developed form. Thus, in 

 Stromatoporella granulata, Nich., as in the closely allied Stromatoporella eifeliensis, 

 n. sp., thin sections show the existence of short, irregularly distributed, vertical 

 tubes, which rarely extend through more than two or three interlaminar spaces, 

 and which are here and there crossed by irregular tabulae. The existence of these 

 tubes can be recognised in both tangential and vertical sections (Plate I, fig. 15, 

 and Plate II, figs. 9 and 10) ; and they appear to open on the surface by elevated 

 tubercles perforated by round apertures (Plate I, fig. 14, and Plate IV, fig. 6.) It 

 can hardly be doubted that we have here an imperfect form of the tabulate zooidal 

 tubes of the typical Stromatoporo3. 



"Well-developed tabulate zooidal tubes, in all respects essentially similar to those 

 of Stromatopora, Goldf., may also be recognised, in a more or less complete form, in 

 such genera as Idiostroma, Winch., and Stachyodes, Barg. 



The forms in which definite zooidal tubes are least developed and least easily 

 recognised as existing at all are those which have usually been regarded as the 

 typical Stromatopora?, namely, those which I shall place under the genus Actinostroma, 

 together with such types as Clathrodictyon, Nich. and Mur. If, for example, we 

 take such a type as Actinostroma clathratum (the Stromatopora concentrica of most 

 authors) and compare the skeleton with that of Hydractinia echinata, Flem., we 

 have little difficulty in recognising the cavities in which the zooids were contained, 

 though definite zooidal tubes such as those of Stromatopora proper are not deve- 

 loped. We recognise, in fact, that anything of the nature of actual tubes is not 

 required by the necessities of the case. In the early condition of the coenosteum 

 in Hydractinia echinata, the outer surface of the horny crust is covered by the 

 coenosarc, as a thin layer from which the zooids are given off. Similarly, in the 

 earliest condition of the skeleton in the genus Labechia, E. and H., there do not 

 seem to have been any superficial apertures ; but the zooids must have been given 

 off from the layer of coenosarc covering the first-formed layer of the skeleton. This 

 is well shown in the example figured in Plate III, figs. 9 and 10, which may be 



