﻿574 ME. A. WILMORE ON THE CARBONIFEROUS [Nov. 10,10, 



poorly developed in the earlier stages, and are often connected to 

 the major septa by thin extensions, now stand oat boldly from the 

 inner boundary of the retreating dissepimental zone. 



The columella persists throughout in all the specimens which I 

 have had cut. It is usually somewhat oval, and is often obviously 

 a thickening of the inner end of the counter septum. It frequently 

 becomes curiously irregular in shape, and, on the other hand, is 

 sometimes almost circular. In those examples where the columejla 

 is strongly compressed, having a cardinal- counter extension about 

 twice that of the lateral extension, a mesial line is often clearly 

 seen, reminding one of the similar appearance in Cyathaxonia 

 rushiana, Vaughan. 



The dissepiments are somewhat variable in their nature and 

 mode of occurrence. In an average specimen they are somewhat 

 as follows : — In the earlier strongly cornute parts of the coral 

 there are very few. In the middle growth-stages they are freely 

 developed, and are more regularly tangential in their orientation. 

 In the later stages they retreat, and form a well-marked dissepi- 

 mental zone, through which the major a^pd minor septa extend. 

 In the final Amplexoid stages they have disappeared. 



The tabulae are irregular in their development, often some distance 

 apart, and varying much in the degree to which they are arched up 

 as they approach the columella. 



Cyathaxonia, Mich. 



Two species are fairly common in the shaly beds, namely: — 

 Cyaihaxonia cornu, Mich., and O. rushiana, Vaughan. 



The occurrence of C. cornu at comparatively high levels seems to 

 be quite regular in Craven ; I have found it in several exposures. 

 As pointed out by Dr. Vaughan, the type-specimen of Michelin 

 was found at Tournai. 1 The two species occur in the same beds 

 at Crag Laithe, as also at Marton School and Gledstone Kennels in 

 a neighbouring district. 



IV. Irregular Distribution of some of the Corals. 



A somewhat remarkable phenomenon is the occurrence of colonies 

 of corals in various parts of the district studied. Some species 

 swarm in one particular place, and are only found sparingly else- 

 where. In quoting instances I will refer also to contiguous districts 

 which have been described in previous papers. 



Zaphrentis ambigua occurs in great numbers in Horrocksford 

 Quarry, Clitheroe, but is much rarer elsewhere. 



Zaphrentis densa is exceedingly plentiful in the shales of Thornton 

 Quarry ; it occurs in several other exposures, but is not common. 



Cyathaxonia rushiana is very common in the shales of Crag- 



1 Quart. Journ. Geol. Soc. vol. lxii (1906) p. 317. 



