84 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 14, 



sions of lamellae : lamellse thick, four markedly prominent, dividing 

 the cavity to a limited extent into four equal parts ; three inter- 

 mediate lamellae, the middle one projecting slightly ; perfect edges 

 within the abdominal cavities attenuated, casts of edges blunt ; 

 crest of lamellae, w^here preserved, sharp, casts obtuse ; lamellae of 

 adjacent cavities sometimes confluent ; sides in contact ; interior 

 composed of small bladder-like cells : young cavities developed at 

 the junction of lamellae belonging to two or more cavities. 



Dr. Fitton describes the Perna beds of the Atherfield section as 

 varying from dark blue sandy clay, or mud, to greenish sand ; and 

 the upper bed from which Cyath. ? elegans was obtained, as differing 

 chiefly in compactness and durability*. To the originally loose con- 

 dition of the deposit, the variations in form presented by the series 

 of specimens may, it is conceived, be chiefly ascribed. When the germ 

 settled upon a Perna or a large fragment of a shell not easily over- 

 turned, the lateral expansion was great compared to the upper growth. 

 In the Museum of the Geological Society is an encrusting specimen 

 presented by Mr. Simms, F.G.S., which measures 3^ inches in one 

 direction and 2 3^ in the other, while the vertical height in the centre was 

 apparently limited to about f rds of an inch. On the contrary, where 

 the base was small, the coral assumed more or less rapidly an hemi- 

 spherical, globular or oval contour. In the first of these forms the 

 shape may be readily ascribed to the arenaceous nature of the bed on 

 which the specimen rested, and which did not allow of a lateral ex- 

 tension ; while the nearly globular or oval examples evidently owed 

 their configuration to a complete or partial inversion, which permitted 

 the living margins to extend over the previous base more or less per- 

 fectly. In such cases the soft portions of the reversed siif faces must 

 have perished, and proofs of such partial destructions were exhibited 

 in many instances. In one case a limited area presented a rugged 

 aspect, the roughness arising clearly from the animal of that part 

 having been killed during the formation of a series of cells ; and the 

 adjacent living polype-matter had been prevented from extending 

 afterwards fully over the dead surface, in consequence, it is conceived, 

 of the latter having been immersed in sand or mud. A weathered or 

 abraded area is easily distinguished from such an exterior by its uni- 

 form smoothness. Amorphous masses plainly resulted from success- 

 ive interferences with development, and probably from an imbedding 

 more or less deeply in sediment. In all these cases Cyath. ? elegans 

 exhibits a similar tendency to marginal expansions, limited or modi- 

 fied in direction by the extent of the body on which the germ origi- 

 nally settled, and the nature of the bed on which the subsequent 

 specimen rested, as well as the liability to be displaced by waves ; but 

 there is an obvious effort to assume an hemispherical contour, when 

 the base was small, and thence one more or less globular. In these 

 respects the fossil agrees with SiderastrcBa, Astrcea, Meandr-ina and 

 other existing corals, provided with a creeping or downward expand- 

 ing, proliferous mantle ; by which the edge of a specimen is constantly 



* Quart. Journ. of the Geological Society of London, vol. iii. p. 294, Aug. 1847. 



