﻿526 MR. R. G. CARRUTHERS OKT THE [Nov. I9IO, 



the centre of the corallum, and a large cardinal fossula ' xpanded 

 towards the inner end 1 (PL XXXVII, figs, 3a-3c). 



The lowest horizon from which specimens have been obtained is 

 the thin bed of limestone exposed at the fork in the stream below 

 Hartsgarth Farm, Xew Castleton. Tbis limestone lies about the 

 middle of the Group, and only yielded a single specimen. 



After a prolonged search by Mr. Macconochie, of the Geological 

 Survey of Scotland, certain beds in the neighbourhood of Larriston, 

 Staneshiel, and Thorlieshope were discovered, from which a con- 

 siderable number of determinable specimens (108 in all) were 

 obtained. These beds lie towards the top of the Group, 300 or 

 400 feet below the base of the Pells Sandstone. 



About two- thirds of the assemblage here found can be referred 

 to Zaphrentis delanouei sensu stricto, but the remainder are of a 

 slightly different type. In their neanic (or adolescent) stage these 

 latter forms agree with Z. delanouei, the fossula being large and 

 expanded inwardly (PL XXXVII, fig. 4 d). As the ephebic (or 

 adult) state is attained, however, the walls of the fossula become 

 parallel (PL XXXVII, figs. 4 b & 4 c) and finally show a tendency 

 to constriction at the inner end (PL XXXVII, fig. 4 a). 



Had these modifications of the original delanouei type of fossula 

 been observed only in a few isolated cases, they might be considered 

 as abnormalities, of no special significance from an evolutionary 

 point of view. But, as they have been noticed in a very considerable 

 number of instances, and, further, recur in the early ontogeny of 

 members of the gens found at higher horizons, they evidently belong 

 to a true mutational form, marking an advance on the parent stock. 

 This mutation may be called Zaphrentis pa rail el a, in allusion 

 to the characteristic fossular outline. 



In Liddesdale, the next coral-bearing horizon above the Cement- 

 stones is the Lawston Linn Limestone, which lies some hundreds 

 of feet above the Fells Sandstone. The limestone overlies a group 

 of thin coals, and is equivalent to either the Dun or the Woodend 

 Limestones of Northumberland, which come above the Scremerston 

 Coals. Prom the Lawston Linn horizon a large number of small 

 corals have been collected. They are so small and irregular in 

 shape, that it is questionable whether any great reliance can be 

 placed on the disposition of the septa (which are usually very thin). 

 The cardinal fossula is often parallel-sided throughout growth, 

 although in manv cases there is a marked constriction of the inner 

 end (PL XXXVII, fig. ] b). The reference of these forms to the 

 delanouei gens is by no means a matter of absolute certainty. 

 Pending a discussion of this question, all that need be stated here 

 is that they are assigned to that gens with some hesitation, and 

 regarded as a side branch from the direct line of evolution. The 

 name proposed for them is Zaphrentis laiustonensis. 



1 A full description of the species is given in Greol. Mag. dec. 5, vol. v (1908) 

 pp. 63 et segq. & pi. v, figs. 5-7. 



