﻿part 4] PHILLIPS 'ASTRAl A HENNA HI, AND ORION AST RJk. A, 



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■Cambridge, the British Museum (Natural History), the Museum 

 of Practical Geology, the collection of the Geological Survey 

 of Scotland, and the Glasgow Museum & Art Gallery; and to 

 Mr. Charles Edmonds, Prof. E. J. Garwood, and Prof. T. F. Sibly 

 for use of the specimens that they had collected. 



My thanks and acknowledgment are also cordially extended 

 to Dr. P. A. Bather, Mr. W. D. Lang, and Mr. C. D. Sherborn 

 for their ever-ready advice and kindly assistance. 



II. Definition of certain Terms employed. 



On account of the unfortunate lack of uniformity in the 

 nomenclature of Corals, it seems advisable, before proceeding 

 farther, to define clearly certain terms here employed. 



I denote the skeleton of a single individual, whether solitary or 

 member of a colony, by the term ' corallite,' and use the term 

 ' corallum ' to mean the skeleton of the whole colony. In the 

 •case of solitary or ' simple ' corals the terms are synonymous. 



I divide the liugose corallite into two regions : (1) the 

 intrathecal region, which is built up of tabulae or of tissue 

 ontogenetically derived from tabula?, and (2) the surrounding 

 ■extrathecal tissue, which is built up of dissepiments. The 

 junction of the tabular with the dissepimental tissue constitutes 

 an annular wall — the theca. The corallite is usually clothed with 

 an outer mural investment — the epitheca, the nature and develop- 

 ment of which I have discussed in a previous publication. 1 



The terminology applied to the septa will be found in a paper 

 by Mr. P. G. Carruthers, 2 or in my own paper ' On the Genus 

 AidopliyUum? 3 



III. The Astr^eiform Corallum. 



Among the Rugose colonial corals there are certain genera, or 

 certain species within a genus, in which the corallites have lost 

 their epitheca, and are united by their dissepimental tissue. 4 



The septa of adjacent corallites in the ' astrseiform ' colony tend 

 to become confluent; but all stages of this development, from that 

 in which it is incipient to that of perfect confluence, are to be 

 found. In some cases, on the other hand, the septa of one 

 -corallite do not extend to those of another, and leave an inter- 

 vening space to the sole occupation of the dissepiments. 



Astrseiform colonies make their ap pearan ce in Avidely 

 divergent stocks and at different periods of time: 

 being, it would seem, the ultimate terms in a progressive deve- 

 lopment along a well-defined line. The steps towards this end 

 are : — 



1 Q. J. G. S. vol. lxxi (1915) pp. 228-29. 



2 Aim. & Mag. Nat. Hist. ser. 7, vol. xviii (1906) pp. 356-63. 



3 Q. J. Gr. S. vol. lxix (1913) pp. 60-62. 



4 An epithecal growth external to the whole corallum may, nevertheless, be 

 retained in the astrseiform colony. 



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