﻿Vol. 66. ] THE EVOLUTION OF ZAPHREXTIS DELANOL'EI. 523 



22. On the Evolution of Zaphrentis delanocei in Lower Car- 

 boniferous Times. 1 By Robert George Carruthers, F.G.S. 

 (Read April 27th, 1910.) 



[Plates XXXYI & XXXVIL] 



Contents. Pace 



I. Introduction 523 



II. Sequence of the Strata 524 



III. Palaeontology 525 



IV. General Succession in the Carboniferous Limestone Series 



(Central Valley of Scotland) 530 



V. Occurrence of the Gens in other Areas 532 



VI. Specific Descriptions 533 



VII. Locality List 535 



I. Introduction. 



An attempt is made, in the following communication, to demon- 

 strate the evolution of a small Zaphrentid coral, belonging to a 

 gens 2 of common occurrence in the Lower Carboniferous rocks of 

 Scotland. 



The simple rugose corals seem to have been strangely neglected 

 by workers on phylogenetic problems. Although suggestions as to 

 the lines of evolution of certain species have been advanced from 

 time to time, no direct proofs have, apparently, been forthcoming. 



Yet, in some respects, few of the Invertebrata are so well 

 adapted for investigations of this nature. In most of these corals, 

 all the growth-stages of the skeleton are retained intact, and can 

 be studied by means of serial sections cut across the corallum. 

 The one serious difficulty arises from the remarkably sporadic 

 distribution of such fossils or, indeed, of the Rugosa in general 

 — a fact only realized to the full after one has engaged in the 

 systematic examination of a wide area, in search of some particular 

 gens. As a matter of fact, the corals here dealt with are the only 

 ones that range through most of the Lower Carboniferous rocks of 

 Scotland. Even then, they are found on horizons often somewhat 

 widely separated in time and unproductive for long distances. 

 Fortunately, the stratigraphy of the Scottish rocks is so well 

 known, that collections can be made all over the country, from 

 horizons the position of which in the sequence is fixed more or less 

 definitely. Although, therefore, section after section of some par- 

 ticular limestone may be searched in vain, the same bed can often 



1 Communicated by permission of the Director of H.JV1. Geological Survey. 



2 This useful term was originated by Dr. A. Vaughan, and defined by him as 

 follows: — 'A gens or species-group may be considered to be the aggregate 

 of all the species which possess, in common, a large number of essential pro- 

 perties, and are continuously related either in space or time' (Quart. Journ 

 Geol. Soc. vol. lxi, 1905, p. 183). 



Q. J. G. S. No. 264. 2 o 



