Vol. 62.I LIMESTONE OF THE MENDIP AREA. 371 



These Clisiophyllids show considerable variation. PI. XXXI, 

 fig. 5 6, illustrates a specimen in which the Cyathophylloid characters 

 are strongly-marked, while fig. 5 a of the same plate illustrates a type 

 with a more markedly Clisiophylloid structure. 



Affinities. — The Clisiophylloid character is exhibited in: — 



A simple Clisiophylloid structure in the central area. In a horizontal section, 

 the central area is small and compressed ; the mesial plate is well-developed, 

 and the concentric tabular intersections are strong and closely packed, but the 

 radial lamella? are few and discontinuous. These characters indicate a central 

 vaulting up of the tabulse, into tall, laterally-compressed cones, which are 

 feebly radiated by lamellae, but conspicuously crested. 



The Cyathophylloid character is shown by : — 



The nature of the septa. The primary septa are numerous and flexuous ; 

 they run inward almost, if not quite, to the central area, and outward to the 

 thin outer wall. The secondary septa are generally well-developed. 



The crowded interseptal vesicles in the medial area, which is radiated by the 

 primary septa only. 



Clisiophyllum. 



Clisiophyllttm aff. curkeenense, Yaughan. 



A form, similar to that which is being described and figured 1 by 

 Dr. A. Vaughan, occurs in the Lower Dibunojphyllum-Zone of the 

 Mendip area. 



Cyclophyllum. 



Cyclophyllum pachyendothecum, Thorns., mut. 



Compare James Thomson, Proc. Phil. Soc. Glasgow, vol. xiv (1883) p. 493 

 & pi. xiv, fig. 1. 



It will be better to await more material, before attempting to 

 describe the detailed characters of our form, which occurs commonly 

 in the Upper Dibunophyllum-ZonQ of the Mendip area. 



(ii) BRACHIOPODS. 



Pro ductus. 



Productus concinno-Martinj. 



Compare Davidson, ' Monogr. Brit. Foss. Brachiop/ (Palaeont. Soc.) vol. ii 

 (1858-63) pi. xliii, fig. 10. (Productus s&mireticulatus, var. concinnus.) 



In this form, which occurs commonly in the Syringothyris-Zono 

 of the Mendip area, the convex valve forms a depressed vault over 

 the flat portion of the concave valve. A section of the valve, taken 

 through the hinge-line, is quadrate, not transverse. 



As suggested 2 by Dr. A. Yaughan, this form may probably be 

 traced back to Productus cf. Martini. Further material and much 

 careful investigation will be necessary, however, before the true 

 relationships of this and other allied forms 3 can be settled with 

 definiteness. 



1 In the present number of the Quarterly Journal, p. 320 & pi. xxx, figs. 2 & 2 a. 



2 Quart. Journ. Geol. Soc. vol. lxi (1905) p. 289. 



3 For example, the strongly-spinose mutation (Productus cf. semireticulatus, 

 mut. S t ) which abounds in the Lower Semmula-Zone. 



