232 Dr. H. A. Nicholson on some new or 



at other times made up of a series of large-sized cylinders, 

 each of which is composed of concentrically disposed layers. 

 The surfaces of successive strata are sometimes smooth, but 

 are at other times covered with low, rounded, closely approxi- 

 mated eminences or " mamelons." Astrorhizse are invariably 

 present and are arranged in superposed groups, each group 

 having a common vertical axial canal. The brandies of the 

 astrorhizEe are sometimes short, sometimes long, but always 

 delicate. The radial pillars are " continuous " and are about 

 ^ to -r\7 millim. apart, as are also the well-marked concentric 

 laminai. The horizontal " arras " given out by the radial 

 pillars appear to be numerous and delicate ; but they are 

 usually not visible at all in tangential sections, or only to a 

 limited extent. Hence such sections do not show the typical 

 " hexactinellid " meshwork of the genus Actinostroma^ but 

 usually closely resemble corresponding sections of the genus 

 Clathrodictyon. 



Ohs. This well-marked species exhibits many interesting 

 and striking variations ; but I shall discuss these fully else- 

 where. It is most nearly related to A. hebhornense^ Nich. 

 [z= Stromatopora astroites^ Barg.). It is, however, distin- 

 guished from this, as from all the other species of Actino- 

 stroma, by the fact that tangential sections (PI. VI. fig. 8) do 

 not show usually the characteristic " hexactinellid " network 

 of the genus. On the contrary, such sections resemble corre- 

 sponding sections of Clathrodictyon in showing the detached 

 ends of the transversely-divided radial pillars either quite 

 separate or partially confluent into vermiculate rows. I have, 

 however, examined specimens in which the typical " hexac- 

 tinellid " structure can be detected in tangential slices, the 

 " arms " given out by the radial pillars being in these cases 

 very numerous, and capillary in point of size. I shall else- 

 where figure the structure in question. The skeletal frame- 

 work is decidedly closer and more dense than in A. hebhornense 

 or A. clathratunij and a marked phenomenon in vertical sec- 

 tions (PI. VI. fig. 9) is the presence of large rounded apertures 

 formed by the cut ends of the radiating astrorliizal tubes. 

 Vertical sections also often show the vertical wall-less canals, 

 from which spring the astrorhizas of successive interiaminar 

 spaces, and round which the concentric laminae are usually 

 bent upwards. 



Formation and Locality. Abundant in the Middle Devonian 

 of the Eifel (Gerolstein and Gees). I have not hitherto re- 

 cognized the species in the Paffrath district. Also abundant 

 in the i\liddle Devonian of Devonshire (Dartington, Lumraa- 

 ton, and Teignmouth). 



