RHABDOMESON. 195 



Surface with circular or longitudinally oval cell -mouths set in quincunx, 

 separated from each other by intervals less than their diameters. Interspaces 

 elevated, ridge-like, bearing nodes or acanthopores on their summits, and three or 

 four mesopores (?) situated generally at the corners of the apertures. About three 

 cell-mouths to 1 mm. 



Size. — A specimen measures 20 mm. long and 1 mm. wide. 



Localities. — Top Orchard Quarry, East Anstey, Ironpost. 



Remarks. — The difficulties in describing this and the following species have 

 been stated above, and the descriptions must be taken as tentative in some 

 respects. 



There is, I think, no doubt that this species is the original Millepora gracilis 

 of Phillips. His enlarged figure accurately represents the appearance that rather 

 worn specimens retaining the surface assume. 



If the Carboniferous Bh. gracile of Young and Young is congeneric, that form 

 would require a new specific name, as it is certainly not identical. 



To the above description it may be added that in some of the natural 

 cylindrical sections showing the central tube there seems a point at which the 

 cells become horizontal, and beyond which they are set obliquely with a slope in 

 the opposite direction to that upon the other side of it. This would appear to 

 be a point of origin, and if so the organism would probably be free. In these 

 specimens I have not seen any signs of branching. 



Affinities. — Carboniferous specimens of " Rhabdomeson gracile " in the Wood- 

 vvardian Museum, from Hook Head and other localities, appear to me to be totally 

 unlike our fossils ; their cells are in perpendicular ranges, their acanthopores are 

 very prominent and bead-like, and I can see no trace of anything like mesopores. 

 Bhombopora dichotoma, M'Coy, sp., 1 and Rhabdomeson rhombiferum, Phillips, sp., 2 

 as represented by specimens in the same Museum, seem quite different in 

 structure from the present fossils. On the other hand, Rhabdomeson interporosum, 

 Phillips, sp., 3 appears, from its specimens, to be very much more like them ; it 

 seems to have mesopores, or at least subsidiary cells or pits of the same character 

 as those in our fossils, and may certainly be regarded as belonging to the same 

 genus. 



1 184-4, M'Coy, ' Synopsis Carb. Toss. Irel.,' p. 198, pi. xxvii, fig. 15. 



2 1836, Phillips, ' Geol. Yorks.,' vol. ii, p. 199, pi. i, figs. 34, 35. 



3 Ibid., p. 199, pi. i, figs. 36—39. 



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