STROMATOPORELLA EIFELIENSIS. 209 



being commonly 2 to 3 centimetres apart. The astrorhizal canals are often fur- 

 nished with transverse partitions or " astrorhizal tabulae ; " but the astrorhizal 

 systems are not superimposed in vertical groups. 



As regards its minute structure, the skeleton-fibre is thick, and is seen in 

 well-preserved examples to be traversed by minute inosculating microscopic 

 tubuli (Plate XI, figs. 1 and 2, and Plate XXVII, figs. 2 and 3 ). Vertical 

 sections (Plate XXVII, fig. 3) show thick and very distinct concentric laminse, of 

 which about six occupy the space of 2 mm. measured vertically. Owing to the 

 thickness of the laminae, the interlaminar spaces are comparatively narrow, and 

 the correspondingly thick radial pillars usually run from lamina to lamina, but 

 do not extend beyond the interlaminar space within which each originates. 

 Definite zooidal tubes are not recognisable. The interlaminar spaces are occa- 

 sionally traversed by a few irregular, curved, calcareous partitions (" interlaminar 

 septa "), but these are never numerous, and may be wanting. Tangential sections 

 (Plate XXVII, fig. 2) show that the skeleton is more completely reticulate than 

 is usual in the genus Stromatojporella. The cut ends of the radial pillars are so 

 far confluent as to give rise to a coarse network, which is traversed by the 

 branches of the astrorhizal canals, and is perforated by rounded or oval apertures 

 representing sections of short zooidal tubes. 



8. eifeliensis, as above defined, has not as yet been recognised in the " Cauno- 

 pora-state." 



Obs. — A careful examination of a very large series of specimens has now 

 satisfied me that in my former description of the species (' Ann. Nat. Hist.,' 

 ser. 5, vol. xvii, p. 235) I embraced two distinct though related types, which 

 differ from one other both in habit and in minute structure. 



One of these forms, to which I shall restrict the name of 8. eifeliensis, is 

 invariably parasitic, and forms thin crusts attached by the whole of the lower 

 surface to foreign organisms, such as Heliolites porosa, Goldf., or, still more com- 

 monly, Bhaphidopora sh-omatoporoitles, Roem. The other form, which I shall 

 describe immediately under the name of *S'. solitaria, possesses a laminar ccenos- 

 teum with an epithecate under surface, and is non-parasitic, being attached by a 

 limited point only. 



The surface of 8. eifeliensis is smooth, and is destitute of " mamelons " 

 (Plate XXVII, fig. 1) ; while it is characterised by the extraordinary develop- 

 ment of the astrorhizal gutters, which are typically so extremely branched as to 

 permit of the free inosculation of adjoining systems. The general aspect of the 

 surface in well-preserved specimens thus closely reminds us of that of Stromato- 

 pora discoidea, Lonsd. The astrorhizaa (Plate IV, fig. 2) are, moreover, usually 

 of large size, and their centres are widely remote. On the other hand, in 8. 

 solitaria the astrorhizse are circumscribed and comparatively small, while they are 



