of Carboniferous Polyzoa. 337 



to set aside Ceriopora has much to commend it ; for the con- 

 fusion of Corals and Bryozoa commenced with Goldfuss. His 

 definition, therefore, is not precise enough, though it is obvious 

 that he founded the genus on a coral. McCoy's restricted 

 genus also belongs to the Corals ; while Morris, by his transfer 

 of the name Ceriopora to a Brjozoon, has left the species under 

 consideration without a generic name to which it has a legiti- 

 mate title. This question of nomenclature is one of great 

 difficulty ,• as, however, the essential character of the fossil we 

 are about to describe separates it from all other known Carbo- 

 niferous forms, we would suggest Rhabdomeson as the generic 

 name, the axis being central, not lateral as in AUman's 

 Rhahdopleura. 



Rhabdomeson gracile (nov. gen.). 



MiUepora gracilis, Phillips, Pal. Foss. 

 Ceriopora gracilis, Mon'is, Catalogue. 



The stem is slender, cylindrical, branching, the branches 

 coming off at right angles to the stem and never less than an 

 inch apart, and consists of a hollow axis formed by a thin 

 calcareous tube, and of a series of cells ranged round the axis. 

 There are 100 cell-apertures in a linear inch ; the apertures 

 are oval, with simple outlines, the funnel-shaped depressions 

 at the bottom of which they are placed sloping down from the 

 crests of the dividing ridges. These ridges are tuberculated, a 

 large tubercle, which well-preserved specimens show to be a blunt 

 spine, being placed at the upper and lower angles of each aper- 

 ture. Hence the periphery of a single cell usually presents 

 four such tubercles, while smaller tubercles occur between each 

 larger pair. But the aperture of the cell does not occupy the 

 whole area of the pore-depression ; a thin lamina reduces the 

 orifice, hymen-like, to one fourth of the area of the pit ; and 

 this restricted orifice is at the upper end of the depression 

 (PI. XVI. B. fig. 4). The cells are conical, the inner extremity 

 being in contact with the axis, the cell tm'ning upwards and out-r 

 wards so that the plane of its aperture is parallel to the axis. 

 The apex of the curved cone terminates two cells and a half 

 below its orifice. Towards their apices the cells are separated by 

 a very thin common wall, which thickens outwards so that the 

 orifices are separated by a partition whose thickness is one 

 third of the diameter of the cell-cavity at its widest })art. 

 When the cells have been removed so as to expose the hollow 

 axis, the wall of the latter is seen to be marked by minute 

 round spots, which at first suggested the possibility of a com- 

 munication existing between the cavity of the cell and that of 



