224 BRITISH STROMATOPOROIDS. 



Amphipoea eamosa, Schulz. Die Eifelkalkmulde von Hillesheim, p. 90, pi. xxii, 



figs. 5 and 6, and pi. xxiii, fig. 1, 1882 (Jahrg. 



d. konigl. preuss. geol. Landesanstalt fur 1882). 



— — Nicholson. Mon. Brit. Strom., Introduction, p. 109, pi. ix, 



figs. 1—4, 1886. 



The coenosteum in Amphipora ramosa is in the form of slender cylindrical stems, 

 from 2 to 7 mm. in diameter, which may be simple, or may branch in a dichoto- 

 mous manner. The surface of the coenosteum is smooth, exhibiting neither 

 " mamelons " nor astrorhizse, and presenting itself under two different aspects 

 (Plate IX, fig. 1). In one series of specimens the surface shows numerous irre- 

 gularly rounded or vermiculate zooidal apertures, with prominent tuberculate mar- 

 gins, giving to the fossil the aspect of a small dendroid Alveolites. In another aeries 

 of specimens the surface is covered with a thin imperforate calcareous membrane, 

 and the fossil looks like a stem of some such coral as Lithostrotion junceum. 

 Partly decorticated specimens may show zooidal apertures over part of the surface, 

 while other portions are covered with a calcareous membrane ; but there is reason 

 to think that the two conditions of the surface are not simply due to the state of 

 preservation, but indicate differences in the state of the organism in different 

 examples (see p. 110). 



As regards the internal structure of the skeleton, the cylindrical coenosteum 

 is traversed by a wide axial tube, which is intersected by transverse or funnel- 

 shaped tabulae (Plate IX, figs. 2 and 4, and Plate XXIX, fig. 4). The general 

 coenosteal tissue is completely reticulate, of the type of that of the Stromatojjoridse, 

 neither radial pillars nor concentric laminae being recognisable as distinct struc- 

 tm-es. The skeleton-fibre (Plate XXIX, fig. 6 a) is apparently solid, without pores 

 or tubuli, each lamina being traversed by a median, dense, and dark-coloured 

 primordial layer, thickened on both sides by lighter-coloured, fibro-crystalline, 

 secondary sclerenchyma, and thus resembling the structure seen in many corals. 



Irregular zooidal tubes radiate outwards from the axial tube, to open on the 

 surface by definite apertures ; but the development of the zooidal tubes is very 

 variable, and they are generally short and sinuous, and are apparently for the 

 most part destitute of tabulae. 



Many examples of Amphipora ramosa have the cylindrical coenosteum sur- 

 rounded by a sheath of large-sized lenticular vesicles, which are' in turn sur- 

 rounded by the delicate imperforate calcareous cuticle above spoken of (Plate IX, 

 figs. 2 and 3, and Plate XXIX, fig. 5). Other specimens either show no traces 

 of marginal vesicles and a bounding membrane (Plate IX, fig. 4), or they may 

 have the marginal vesicles imperfectly developed and of small size (Plate XXIX, 

 figs. 6 and 7). The significance of the above variations of structure cannot be at 

 present fully estimated ; but it is possible that the marginal vesicles are connected 



