﻿Yol. 66.] EVOLUTION OF ZAPHRENTIS DELANOUEJ. 537 



EXPLANATION OF PLATES XXXVI & XXXVII. 

 Plate XXXVI. 



Fig. I. General section of the Lower Carboniferous rocks of Scotland. 



2. Geological sketch-map of Scotland south of the Great Glen, showing 

 the distribution of Carboniferous fossil localities, on the approxi- 

 mate scale of 26 miles to the inch. 



Plate XXXVII. 



[All figures, except figs. 1 & 2, are from camera-lucid a drawings, X 2*5 

 diameters. Figures with the same numeral represent serial sections from one 

 corallum.] 



Fig. 1. A typical member of the gens, showing the external characters. 

 Auchenskeith Quarry, Ayrshire (Lower Limestones, Hurlet 

 horizon). Natural size. 

 2. Another specimen. Middlehope Hill Quarry, Fauldhouse (L T pper Lime- 

 stones, Calmy horizon). Natural size. 

 Figs. 3a-3c. Zaphrentis delanouei. Thorlieshope Quarry, Liddesdale (Ce- 

 mentstone Group). 

 4 a-4 d. Zaphrentis parallela, sp. nov. Larriston Quarry, Liddesdale 



(Cementstone Group). 

 ba-od. Zaphrentis constricta, sp. nov. Duloch Quarry, Dunfermline 

 (Lower Limestones). 



6 a-6 e. Zaphrentis disjuncta, sp. nov. Early form (pseudo-^ara^a). 



Crosshouse Quarry, East Kilbride (Lower Limestones, Hui'let 

 horizon). 



7 a-1 e. Zaphrentis disjuncta, sp. nov. Typical form. Orchard Quarry, 



Glasgow (Upper Limestones). 



8 a-8 d, Zaphrentis disjuncta., sp. nov. Advanced form. Middlehope Hill 



Quarry, Fauldhouse (Upper Limestones, Calmy horizon). 

 Fig. 9. Zaphrentis lawstonensis, sp. nov. Vertical section. Lawston Linn 



Limestone, R. Liddel, a quarter of a mile below Kershopefoot. 

 Figs. lOa-lOc. Zaphrentis lawstonensis, sp. nov. Lawston Linn Limestone. 



Same locality as above. 



Discussion. 



Dr. A. Vatjghan heartily congratulated the Author upon the 

 completion of an exceptionally fine piece of work, demanding 

 the highest powers of observation, combined with the exercise of 

 untiring patience. The variation in the gens of Zaphrentis 

 delanouei might now he regarded as definitely known in the 

 Lower Carboniferous of Scotland ; in other parts of the British 

 Isles, the facts, so far as they were yet known, were in agreement. 

 It did not admit of question that the determination of a con- 

 siderable number of such genetic series for the coral gentes of 

 commonest occurrence in the Lower Carboniferous would form the 

 base of an ideal time-scale or zonal series. The Author had 

 shown that this ideal was attainable in a gens whose very 

 simplicity of structure constituted its great difficulty ; the more 

 complex gentes would probably yield more readily to less effort. 



The system of zoning at present in use was based upon such 

 obvious characters as first establishment and dominance of certain 

 species (pretending iu no way to genetic relationship) and, ulti- 

 mately, upon the identity or similarity of faunal assemblages. 

 Such a system had admittedly the defects of its simplicity. It had 



