460 Mr. J. Thomson and Dr. H. A. Nicholson on the 



connected with the central area. As exhibited in longitudinal 

 sections (PL XXIII. fig. 1) the central area in these forms is 

 constituted by a succession of extremely close-set tabulae, some- 

 what concave, with their convexities directed downwards, and 

 intersected by two or three parallel, nearly continuous columel- 

 larian lines. (2) As exhibited in transverse sections (PI. XXIII. 

 figs. 1 A, 2, 3 A, 4) the central area is seen to be formed by 

 the tabulge just mentioned, together with a series of vertical 

 lamellee which (as in Clisiophyllum and Dihunophyllum) are 

 wholly independent of the primary septa, except so far, that 

 they are occasionally connected with them by subconvolute 

 plates. The cut edges of these lamellae, as seen in section, 

 show that their number is comparatively small, and that they 

 radiate, usually without twisting, from the margins of the 

 central area towards the centre ; whilst they are united late- 

 rally by a number of closely arranged curved lines, repre- 

 senting the cut edges of the tabulae, and invariably directed 

 with their concavities outwards. (3) The median member of 

 this comparatively small system of vertical lamellae is inva- 

 riably the most strongly developed of all, but it never extends 

 across the central area as a complete mesial septum (as in 

 Dihunophyllum). It is invariably directed towards the dorsal 

 or convex side of the corallum, and is continued in all cases 

 for a certain distance into a well-marked septal fossula. (4) As 

 the consequence of the peculiarities in the internal structure 

 of the central area in Aspidophyllum^ the resulting eminence 

 in the floor of the calice presents certain features which readily 

 distinguish it from the same eminence in Clisiophyllum and 

 Dihunophyllum. The calicine boss (PL XXIII. figs. 2 A, 5) 

 constitutes a prominent helmet-shaped eminence, which is 

 neither conical as in Clisiophyllum ^ nor simply rounded as in 

 Dihunophyllum^ but is dome-shaped on the ventral or con- 

 cave side of the corallum, and slopes down on the dorsal or 

 convex side to the inner margin of the primary septa. The 

 free edges of the vertical lamellge of the central area appear 

 on the surface of the boss as so many keeled ridges, which 

 are not spirally bent as in Clisiophyllum, and do not meet 

 on the two sides of a central ridge as in Dihunophyllum. 

 The median ridge, however, representing the median lamella, 

 passes over the boss, and descends into the fossula on the 

 dorsal side of the corallum. 



So far as our present researches have extended, the corals 

 which belong to this section are confined to the Lower Carbo- 

 niferous rocks. 



