III. On the structure and affinities of guynia annulata, dunc., with remarks upon the persistence of palaeozoic types of madreporaria

Abstract

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 1860†. 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 cænenchyma. 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 synapticulæ attached to their laminae. The individual corallites multiply by gemmation, and do not undergo fissiparous division. The reproductive buds usually grow upon the calice of the parent, whose growth they arrest, and thus a superposition of generations is induced. In some genera the gemmation is lateral." This section of the Madreporaria necessarily included a great number of genera; and as they all could be readily distinguished from those of the other great sections, the new arrangement was adopted by palaeontologists.