﻿Vol. 66.~] LI31ESTONE SOT/TH OF THE CKAVEN EATJLT. 58 L 



In the first place, I conclude from the examination of hundreds 

 •of specimens that the three species, reticulata, geniculata, and 

 ramulosa, should be regarded as passing by insensible gradations one 

 into the other. Whether on this account they should be included 

 in a ' circulus,' or whether they should still be classed as species, 

 will no doubt be decided by the test of general convenience in this, 

 as in other cases. 



The central type in the Craven Lowlands is a somewhat loose 

 reticulate form, tending slightly towards the S. laxa of Phillips. 

 The corallites measure about a millimetre and a half in average 

 thickness, and are rather more than that distance apart. The 

 connecting tubuli are somewhat irregularly distributed, and they 

 are seldom appreciably verticillate in their origin. There is a 

 very small amount of dichotomous branching, the new corallites 

 arising from' the transverse connecting tubes. The amount of 

 geniculation is extremely variable, but there is often a distinct 

 bending towards the neighbouring corallite at the point of origin 

 of the cross -tubes. 



This central type occurs in the beds below the common Caninia 

 aft*, gigantea, in the Eshton-Hetton anticline. It seems to vary 

 laterally, that is, at or about the same horizon, so far as I can make 

 out, in two directions. On the one hand, in the direction of Hetton, 

 the corallites become smaller, rather more closely packed, and more 

 inclined to open directly into each other. Thus the sections and 

 surface-views of weathered specimens show a somewhat Ealysites- 

 like appearance. 1 I have seen as many as nine corallites opening 

 one into the other, forming a sort of chain. In some cases a 

 common visceral cavity of some considerable relative size is 

 formed. 



On the other hand, in the direction of Bell Busk and Swinden 

 Moor, there seems to be an increase in the number of coralla, which 

 are made up of rather smaller corallites with much thicker walls. 

 The corallites in these examples are more irregular in their distance 

 apart, but the distance is usually greater. The number of con- 

 necting-tubes become less, and the amount of dichotomous branching 

 increases. Thus the tendency is towards a ramulose form. at this 

 -horizon, but I think that no one would class the coralla as belonging 

 to S. ramulosa, as defined by Goldfuss. 



In those beds which are, in all probability, higher in the series, 

 another mutation is seen. In the beds of the knoll region which 

 are sometimes classed as D 3 , Syringopora is comparatively rare ; 

 but the specimens which I have found exhibit very sharply defined 

 characteristics. Without exception, the ramulose character is now 

 less evident, and the reticulate character more developed. Most of 

 the specimens have parallel tubes, showing remarkable regularity 

 of distribution. Specimens from Swinden and Elbolton have 

 much of the appearance that led to the adoption of the species 

 S. parallela. 



1 Cf. Dr. Vaughan's Syringopora cf. reticulata in Quart. Journ. Geol. Soc. 

 vol. lxi (1905) p. 268. 



