ACTINOSTROMA HEBBORNENSE. 137 



appear to be thickened, and the intervening pores then assume a roundish shape. 

 German specimens, so far as I have seen, always have the concentric lamina? placed 

 at a greater distance apart than is the case with English examples (compare 

 figs. 7 and 5 in Plate XIII), but there is no other marked difference to be noted. 



Distribution. — Actinostroma bifariiim is only known as occurring in the Middle 

 Devonian. The species is not rare in the pebbles of Devonian Limestone in the 

 Triassic conglomerates of Devonshire (Teignmouth, &c). In Germany it has not 

 hitherto been found except in the Paffrath area, occurring not very rarely at 

 BCichel. I have figured the minute structure of the German examples, as all the 

 British specimens which I have examined are more or less extensively affected by 

 crystallisation, and usually somewhat distorted by pressure. 



4. Actinostroma hebbornense, Nich. PI. XVI, figs. 9 — 16. 



Stromatopora astroites, Bargatzky. Die Stromatoporen des rheiniscken Devons, 



p. 56, 1881. (Non Stromatopora astroites, Rosen.) 

 Actinostroma hebbornense, Nich. Ann. Nat. Hist., ser. 5, vol. xvii, p. 228, pi. 



vii, figs. 7 and 8, 1886. 



The ccenosteum in this species is massive, often of large size, and apparently 

 non-epithecate. The skeleton is very regularly laminated, and the surfaces of the 

 laminae are smooth and devoid of " mamelons." The astrorhizal system is exten- 

 sively developed, the laminae showing numerous large branching astrorhizae (Plate 

 XVI, fig. 9), the centres of which are usually from 6 to 8 mm. apart, and which 

 may or may not be arranged in vertical groups. 



As regards the internal structure of the skeleton, the radial pillars are very 

 slender and are straight; and as definite " latilaminae" are not developed, they run 

 for indefinite distances. Usually about five radial pillars occupy the space of a 

 millimetre, but in some examples they are closer than this. The concentric 

 laminae are well marked, and there are generally about four (sometimes five) inter- 

 laminar spaces in one millimetre. The radial pillars give out radiating " arms " in 

 very regular whorls, each whorl generally consisting of four or five spokes, and 

 the union of these gives rise to a very regular angular meshwork (Plate XVI, 

 figs. 10 and 11). 



Obs. — Actinostroma hebbornense was identified by Bargatzky with Actinostroma 

 {Stromatopora) astroites, Rosen sp. ; but I have examined the original specimens of 

 both species, and find them to be quite distinct. In its general structure A. 

 hebbornense is closely related to A. clathratum, Nich., with which it agrees in intimate 

 structure and also in its mode of growth. It is, however, clearly distinguished 



