﻿Vol. 64.] CARBONIFEROUS LIMESTONE OF THE MIDLAND AREA. 73 



in the Midland area. It is locally abundant in the uppermost beds 

 of that subzone, and probably ranges into B^. 



Comparison with other Species. — Lonsdalia jioriformis 

 (Flem.) differs from L. duplicata in its usually massive habit of 

 growth, and also in the following structural details, as seen in a 

 horizontal section : — 



(1) The central area is, as a rule, finely reticulate in structure, with numerous 



radial lainelljae, and is sharply bounded. 



(2) The primary septa are not so strongly thickened; and a secondary 



series is usually well developed. 



(3) The inner wall is less strongly thickened, and the external area, radiated 



by the septa, is broader and more constant. 



(4) The vesicles of the peripheral area are usually smaller. 



Lonsdalia rugosa, M'Coy, resembles L. duplicata in its dendroid 

 habit of growth, but is widely different ^ in internal structure. As 

 seen in a horizontal section, no purely -vesicular peripheral area is 

 developed ; all the septa extend to the outer wall ; and the external 

 dissepimental area is very broad. 



The simple Clisiophyllids. 



The following descriptions do not include any account of those 

 very interesting corals, belonging chiefly to the genera Histiopliyllum^ 

 JRhodopTiyllum, and CymatiopJiyllum, which I have found to occur 

 in great abundance in the Lonsdalia-suhzone of the Midland area. 

 I had originally intended to include a description of these forms in 

 the present paper ; and with that intention, I had sections cut of a 

 large number of specimens. These corals, however, exhibit such 

 remarkable variation that a satisfactory description of their relation- 

 ships will involve prolonged study, and must be of considerable 

 length. I have decided, therefore, to defer the description of them ; 

 but I hope soon to describe and figure the important Midland types 

 in a separate communication, supplementary to the present paper. 



Clisiophyllum, Dana (pars) ; Thoms. & Nich.^ 

 Clisiophylltjm aff. M'Coyanum, Thomson. (PI. I, fig. 4.) 



Description. — The form is elongate-conical. 



In a horizontal section : — The large, subcircular, central area 

 is finely reticulate in structure, numerous thin radial lamellae, 

 which are distinctly curved spirally, being united by closely-set 

 tabular intersections. The strong mesial plate falls considerably 

 short of the circumference of the area on either side. 



^ The inclusion of ' Lonsdalia ' rugosa in the same genus with L. fiorifoo-mis 

 and L. duplicata is open to great objection. The absence of a peripheral 

 purely-vesicular area, the strong development of the external dissepimental 

 area, and the complete (or nearly complete) bisection of the central area by the 

 mesial plate, are essential characters of M'Coy's species, which, taken together, 

 call for its generic separation from Lonsdalia Jioriformis and L. duplicata. 

 ^^2 For a full description of" the genus Clisiophylhim^ and an explanation of 

 th€ terms employed in describing the Clisiophyllids, see J. Thomson & 

 H. A. Nicholson, Ann. & Mag. Nat. Hist. ser. 4, vol. xvii (1870) pp. 451-57. 



