﻿282 



DE. STANLEY SMITH ON AULINA ROT1 FOBMIS, [vol. lxxii, 



1. The simple or solitary coral. 



2. The fasciculate colony, in which the corallites are not contiguous or do 



not press on one another, and are therefore cylindrical in form, aa 

 (for example) Lithostrotion martini. 



3. The basaltiform colony, in which the corallites are contiguous, and 



are prismatic through mutual pressure. Although the corallum is 

 massive, the corallites are defined by an epitheca, as (for example) 

 Lithostrotion basaltiforme. And, finally, 



4. The astrseiform colony : for instance, Orionastrsea. 



The examples quoted are from a single lineage. 



The number of genera represented by the astrseiform type of 

 colony among the Rugosa does not appear to be numerous at any 

 period, although the individuals may be extremely abundant. 1 



Strombodes is fairly common in the Upper Silurian ; Phillips- 

 astrcea is very plentiful in the Upper Devonian ; while, among 

 the British Carboniferous Rugosa, the only examples of astrseiform 

 genera and species that have come under my notice ai'e Aulina and 

 Orionastrcea, Cyathophyllum regium Phillips, and a species of 

 KonindcopJiyllum (or Diphyphyllw/ni). All these forms are from 

 the uppermost part of the Carboniferous Limestone Series — D 2 and 

 higher beds. 



Certain Characters assumed by the Astiseiform Coral] urn in 

 the Rugosa, and Factors that have produced them. 



The coralla of Orionastrcea and of Aulina exhibit certain 

 interesting characters — namely, a flattened form, an extensive 

 development of extrathecal tissue, and epithecal growth external 

 to the colony, even in cases where there is no trace of epitheca 

 within it. 



(i) The form of the corallum is correlated with the mode of 

 growth of the corallites. These may arise at any point 

 on the surface of the corallum, but the region of most 

 active growth is the margin. The peripheral corallites at 

 first grow outwards, away from the centre of the colony, 

 and then bend upwards into a more vertical position, as is 

 shown in fig. 1 (p. 283). 



The extreme case of this form of colony is to be found, not 

 in the Rugose but among the ' tabulate ' corals — for example, 

 HeJiolites, where an almost horizontal base is often developed. 



1 This type of corallum, while exceptional in the Rugosa, is characteristic 

 of the massive Aporose corals — in fact, exceptions are rare, — but it must be 

 remembered that the epithecal covering to the skeleton (always present in 

 Rugose simple corals) is often lacking in the case of Aporose simple corals. 

 The maeandrifbrm colony (due to repeated but incomplete fission so common 

 among the Aporose stocks) is unknown in the Rugosa, and necessarily so, on 

 the assumption that Rugose colonies increase by gemmation only, but never by 

 fission. (See my notes on the subject in Q. J. Gr. S. vol. lxxi, 1915, p. 233, 

 and W. D. Lang-, ' Homoeomorphy in Fossil Corals ' Proc. Geol. Assoc. 

 vol. xxviii, 1917, p. 90.) 



