210 BRITISH STROMATOPOROIDS. 



arranged in vertically superimposed systems. Each of these systems, further, 

 becomes surrounded in 8. solitaria by an " astrorhizal cylinder," similar to what 

 is seen in Actinostroma verrucosum, Goldf. Hence the surface exhibits con- 

 spicuous conical prominences or " mamelons " (Plate XXVII, fig. 4). 



Again, as regards the minute structure of the ccenosteum, though the concen- 

 tric lamina? have much about the same closeness in the two species, these struc- 

 tures are much more delicate in S. solitaria than they are in 8. eifeliensis, the 

 interlaminar spaces of the former thus becoming comparatively much wider and 

 more open (compare figs. 3 and 7, Plate XXVII). 



Lastly, the skeletal tissue is much less completely reticulated in 8. solitaria 

 than it is in 8. eifeliensis, while there exist perforated tubercles of the same 

 character as those seen in 8. granulata, Nich. 



As above restricted, 8. eifeliensis becomes an exceedingly natural and well- 

 defined species of Stromatoporella ; and the only other form of the genus with 

 which it could be confounded is 8. arachnoidea, Nich., which occurs associated 

 with it. This latter species (' Aun. Nat. Hist.,' ser. 5, vol. xvii, p. 237, pi. 

 viii, figs. 1 and 2) is, however, distinguished from 8. eifeliensis not only by its 

 non-parasitic habit, but also by the extraordinary development of the " inter- 

 laminar septa," which give to both tangential and vertical sections of the 

 ccenosteum an altogether unique and characteristic appearance. 



Distribution. — 8. eifeliensis occurs abundantly in the Middle Devonian of 

 Gerolstein, in the Bifel. I have not certainly identified the species as occurring 

 in the corresponding rocks in Britain, the form which I doubtfully referred to 

 this species (' Mon. Brit. Strom.,' pi. ii, figs. 9 and 10) being rather referable 

 to tb,e type which I now call 8. solitaria. 



6. Steomatopokella solitaria, n. sp. PL VII, fig. 4, and PI. XXVII, figs. 4 — 7 ; 



(?) also PI. II, figs. 9 and 10. 



Stromatopoeella eifeliensis, Nicholson. Mon. Brit. Strom., pt. 1, pi. vii, 



fig. 4 (figure only) ; and woodcut, 

 fig. 7, 1886. 

 — — (pars). Ann. Nat. Hist., ser. 5, 



vol. xvii, pi. viii, figs. 5 and 7 

 (not fig. 6), 1886. 



The ccenosteum in this species is of considerable size, laminar in form, with a 

 basal epitheca, attached at one point only, not parasitic. The thickness of the 

 ccenosteum is from two to nearly three centimetres. The surface (Plate XXVII, 

 fig. 4) exhibits prominent conical eminences or " mamelons," the centres of which 



