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III. On the Structure and Affinities of Guynia annulata, Dune., with Remarks upon the 
Persistence of Palaeozoic Types of Madreporaria. By P. Martin Duncan, M.B. 
Lond., F.R.S., Professor of Geology in King's College, London. 
Received March 16, — Read May 4, 1871. 
Contents. 
I. Introduction 29 
II. The description of the genus Guynia and the species Guynia annulata 32 
III. The affinities of the species with the Palaeozoic Cyathaxonidce 32 
IV. The differentiation from Haplojohyllia paradoxa, Pourtales, and the position of this 
species in the Cyathaxonidce 33 
V. The affinities of Conosmilian species with the Stauridce and Cyathaxonidce 34 
VI. A notice of the secondary stony Madreporaria with Palaeozoic affinities 36 
VII. Conclusion 38 
VIII. Explanation of the Plate 39 
I. During their comprehensive study of the Fossil Corals of the Palaeozoic rocks, 
MM. Milne-Edwards and Jules Haime were impressed with the necessity of founding 
the great section of the Madreporaria called the Rugosa ; they established the section 
in 1850*, and confirmed its differentiation in 186 Of. The characters of the Rugosa were 
then decided to be as follows : — “ In this division, which comprehends simple as well as 
compound corals, the septal structures never form six distinct systems . . . and appear to 
be referable to four primitive elements. Sometimes this arrangement is evidenced by 
the great development of four principal septa, or by the existence of a corresponding- 
number of depressions which are seen at the bottom of the calicular fossa and which 
give a crucial appearance to it. In other instances one depression or one large septum 
exists so as to interrupt the perfection of the septal star. Occasionally no groupings or 
systems can be distinguished ; and the septa are represented by striations which rise up 
on the upper surface of the tabulae, or by endothecal vesicles which may be observed on 
the inner side of the wall. The corallites are always distinct and separate from each 
other, for they are never united by an independent ccenenchyma. The wall is usually 
feebly developed. The visceral chamber is usually occupied by a series of tabulae, or by 
vesicular endotheca, which often constitutes the bulk of the corallum. The septa, 
although often incomplete, are never porous or spongy, and they are rarely granular, 
and never have synapticulae attached to their laminae. The individual corallites multiply 
by gemmation, and do not undergo fissiparous division. The reproductive buds usually 
* Monograph of the Rritish Fossil Corals. London, 1850, Palseontographical Society. 
f Histoire Naturelle des Coralliaires. Paris, 1860. 
