FAMILY ACTINOSTROM1P.E. 131 



Family— ACTINOSTROMID^]. 



Genus 1. — Actinostroma, Nicholson, 1886. 



(Introduction, p. 75.) 



1. Actinostroma clathratum, Nich. PI. I, figs. 8 — 13, and PI. XII, figs. 1 — 5. 



Steomatopora concentrica, M'Coy (?). Brit. Pal. Foss., p. 65, 1851. 



— — Bargatzky. Die Stromatoporen des rheinischen 



Devons, p. 54, 1881. 



— — Freeh. Zeitschr. der deutsch. geol. Gesell , Jahrg. 



1885, p. 116. 

 Actinostroma clathratum, Nich. Monogr. Brit. Strom., General Introduction, 



p. 76, pi. 1, figs. 8—13, 1886. 

 — — Nich. Ann. Nat. Hist., ser. 5, vol. xvii, p. 226, pi. 



vi, figs. 1—3, 1886. 



Coenosteum massive, usually spheroidal or globular, but very irregular in form, 

 and sometimes attaining a large size (Plate XII, fig. 1). The base of attachment 

 is small and the under surface is not epithecate, as a general rule. In many cases 

 the process of growth was intermittent, and the skeleton thus comes to consist 

 of more or less conspicuous concentric strata or " latilaminae." The concentric 

 laminae are simply curved or are but slightly undulated, and the surface is, 

 therefore, smooth and free from pointed eminences or " mamelons." In well- 

 preserved examples the surface exhibits numerous rounded tubercles — the upper 

 ends of the radial pillars — connected by radiating " arms," which enclose angular 

 or rounded meshes— the apertures of the zooidal pores. Less well-preserved 

 specimens (Plate II, fig. 11)] show simply the rounded tubercles. 



Astrorhiza3 may be present, in which case they are mostly quite inconspicuous, 

 and are hardly recognisable except in thin tangential sections. In one variety 

 astrorhizae are comparatively numerous, and in some cases they appear to be 

 wholly wanting. 



As regards internal structure the radial pillars are " continuous/' each pillar 

 passing without interruption through several successive laminae (Plate XII, figs. 3 

 and 4). On an average there are from three to four radial pillars, and the same 

 number of interlaminar spaces in the space of 1 mm. The pillars and concentric 

 laminae are thus about \ mm. more or less apart. The radial pillars are connected 



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