﻿532 MR. E. G. CAEEUTHEES ON THE [NOV. I9IO, 



future work ; in all probability, a close examination of such well- 

 known datum-lines as the Hurlet and Calmy Limestones would 

 eventually yield good results. 



To summarize: the map (PI. XXXVI, fig. 2) and fossil lists 

 appended to this paper bring out the fact that assemblages from 

 the two great Limestone Groups are everywhere separable on an 

 evolutionary basis ; while, for some reason or other, the proportion 

 of ZapJireniis disjuncta increases within the Lower Group in cross- 

 ing the Central Valley of Scotland from east to west. 



The questions involved in this last fact are of great interest, but 

 they do not affect the main thesis, that a gradual evolution of the 

 whole gens occurred during Lower Carboniferous times. 



Y. OcCUEEENCE OF THE GENS IN OTHEE AEEAS. 



Zaplirentis delanouei seems to be common at Tournai, and also 

 in the South- Western Province, where Dr. Vaughan has found that 

 the species is an abundant and characteristic fossil in the Z 1 sub- 

 zone. Above that position the gens seems to have been extin- 

 guished by unfavourable conditions. 



Some half-dozen specimens which I collected from the Z x sub- 

 zone at Burrington are all referable to Z. delanouei sensu stricto. 



On account of the prevalence of the parallela mutation in the 

 Upper Cementstones of Liddesdale, I should place the latter rather 

 higher in the zonal sequence — perhaps in the C zone. The distance 

 of the limestones from the base of the Carboniferous, as well as 

 other lines of evidence that need not here be discussed in detail, 

 lend some support to that opinion. 



Z. consiricta has been found by Prof. Garwood at the top of the 

 massif (D 2 ?) in Westmorland. The species also appears to occur 

 in Derbyshire, since it is represented by a syntype of M'Coy's 

 species Zaplirentis costata (described as Cyatliaxonia costata in ' Brit. 

 Pal. Foss.' 1855, pi. iii c, fig. 2). 1 



Zaplirentis disjuncta is represented in internal casts from the 

 Millstone Grit of Congleton Edge (Cheshire). These specimens are 

 in the Geological Survey Collection at the Museum of Practical 

 Geology, Jermyn Street, London. 



Zaplirentis lawstonensis is found at Woodend Quarry (Northum- 

 berland) and at Biteabout, a mile and a quarter south-west of 

 Lowick ; and I have also obtained a single specimen from the Dun 

 Limestone on the coast south of Berwick-on-Tweed. Both of 

 these localities are close to the Lawston Linn Limestone in strati- 

 graphical position. 



Most of the specimens examined in this investigation have been 

 personally collected in the field. A good number, however, were 



1 I am much indebted to the authorities of the Sedgwick Museum, Cam- 

 bridge, for permission to cut this specimen, previously whole. In. view of the 

 latter fact, I have taken the other syntype, which showed the septal disposition 

 characteristic of M'Coy's species, and was figured by him (loc. supra cit. 

 fig. 2 a) for that purpose, as the holotype of Z. costata. 



