VAUGHAN : CLISIOPHYLLUM INGLETONENSE. 
253 
II. Comparison with CUsiophyllum Dana. 
As a typical species of CUsiophyllum, I select C. omaliusi 
Haime, figured in this paper (PI. XXXVIII., Figs. 
2a, 2b) ; this species agrees with the definition given 
by Dana in " Xarr. U.S. Explor. Exped.," 1838-42, 
Vol. VII., Zoophytes, p. 355, and pp. 361, 362. 
Our species agrees with CUsiophyllum in the large reticulate 
central area and in the septate external area. 
It differs in having a strong mesial plate^ and well marked 
boundary waUs between the several areas. 
CONCLUSIONS. 
CUsiophyllum ingletonense may therefore be said to be a 
CUsiophyllum wdth strong convergence toward Carcinophyllum, 
particularly in the young stages. 
It belongs to a sub-division, the nucleated Clisiophylla, 
characterised by the differentiation of the central area into nucleus 
and aureole ; this group is, however, probably diphyletic {vide 
infra.). 
Nucleated Clisiophylla already figured 
from the base of the Visean (C-S). 
Sj, Blackstone Point (near Amside) ; figured by Prof. E. J. 
Garwood in Q.J.G.S.^ 
This form is very near our species, certain sjoecimens 
being identical. 
Sj, Carlyan Rocks, Rush (Co. Dublin) ; figured by myself in 
Q.J.G.S., Vol. 64, PI. 49, Fig. 1. 
Differences : the aureole is indistinctly marked off from 
the medial area. 
Sj, VaUis Vale, E. Mendips ; figured by Dr. T. F. Sibly in Q. J.G.S., 
Vol. 62, PI. 31, Fig. 5a. 
Differences : — The external area is Cyathophj^lloid and 
the aureole indistinctly marked off from the medial area. 
Evolution of the nucleated Clisiophylla. 
From CUsiophyllum omxiUusi (described below), it is easy to 
imagine the derivation of the Cyathophylloid CUsiophyllum 
described by Dr. Sibly from S^ of the Mendips (v. s.), for con- 
1 In CUsiophyllum the cardinal lamella ks, however, usually produced across the centre and 
somewhat thickened. 
2 Paper read but not yet published. 
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