STROMATOPORA BtJCHELIENSIS. 187 



lobate form (Plate X, fig. 5), and of comparatively small size. Massive specimens, 

 however, are not uncommon, and these may attain a diameter of several inches. 

 The laminar form of ccenosteum is very rare, but is not absolutely unknown. 

 Many specimens, again, consist of elongated, finger-like cylinders (Plate XXIII, 

 fig. 4), which may be more or less isolated and separate, or which may be 

 partially or wholly enwrapped and bound together by a common sheath of 

 coenosteal tissue (Plate XXIII, fig. 5). Bach cylinder has the zooidal tubes 

 vertical in the centre, but bent outwards marginally so as ultimately to open on 

 the surface more or less nearly at right angles to the axis of the growth. Indi- 

 vidual cylinders vai*y in diameter from 1 to 2 cm. Examples with the peculiar 

 mode of growth just described are so characteristic that they may be distinguished 

 by a special title as 8. Biicheliensis, var. digita.ta, Nich. 



The surface of 8. Biicheliensis is without eminences or " mamelons," and the 

 astrorhizas are characteristically small and remote. These structures are not 

 placed in vertically superimposed systems, nor are astrorhizal cylinders, even in 

 the digitated variety of the species, ever developed. As regards its internal 

 structure, the present species has the porous skeleton-fibre and the completely 

 reticulate coenosteal tissue of all the species of Stromatopora. The skeleton-fibre 

 is comparatively slender, and the skeletal network is of a close character, the 

 zooidal pores being mostly oval or elongated ; the zooidal tubes are very numerous 

 and well developed, and are generally furnished with numerous transverse tabular 

 (woodcut, Fig. 20, d). 



8. Biicheliensis occurs very commonly in the " Caunopora-state." The 

 " Caunopora-tubes " are usually very small, perhaps from -fa to -fa mm. in 

 diameter ; but in some specimens the tubes may be as much as from J to | mm. 

 in diameter. Very generally the Caunopora-tubes show distinct funnel-shaped 

 tabula?, and in some cases they also possess short septal spines. 



S. Biicheliensis is more nearly related to 8. Hiipschii, Barg., than to any other 

 species of the genus Stromatopora. It is, however, readily distinguished from the 

 latter by its much finer skeleton-fibre and the correspondingly closer texture of 

 the skeletal tissue ; while the astrorhizge are more remote and are more definitely 

 circumscribed than is the case in 8. Hiipschii. From 8. typica, Rosen, the present 

 species is likewise distinguished by its more delicate skeleton-fibre and the much 

 more limited development of the astrorhizse. From 8. florigera, Nich., the species 

 is readily separated by the remoteness of the astrorhizae, as well as by the fact 

 that these structures are not placed in regular vertical systems, while the skeletal 

 network is also finer and closer. 



Distribution,— 8 . Biicheliensis, Barg., appears to be wholly confined to rocks 

 of Middle Devonian age, and is a common species both in Britain and the 

 Continent of Europe. Both the ordinary lobate or massive forms of the species 



