﻿ATHYRIS. 



S5 



circular aperture, and the spiral appendages for the support of the oral arms have their 

 extremities directed outwards, and are united by a complicated system of lamellae. • 

 Dimensions and relative proportions very variable j two specimens have measured — 

 | Without the spinose expansion, length 24, width 33, depth 15 lines. 

 [With ditto „ 32, „ 39, „ 17 „ 



Without ditto „ 24, „ 26, „ 16 „ 



With ditto „ 31, „ 32, „ 17^ „ 



Some examples have even slightly exceeded these dimensions, but the generality of speci- 

 mens are much smaller. 



Obs. This remarkable species has been often confounded with Athyris plano-suleata. 

 but from which it is easily distinguished by its spines, which are very different from the 

 numerous large, concentric, lamelliform expansions of A. plano-sulcata ; and it is from the 

 generality of palaeontologists having overlooked this circumstance, that they have so often 

 confounded the two shells. So closely packed are the spinose ridges which invest the 

 entire surface of A. Boy$$ii, that no portion of the surface of the valve itself can be perceived, 

 and I have counted as many as eighty of these pectinated fringes on one of the valves of 

 a specimen which did not measure more than ten lines in length by thirteen in width. 

 This arrangement will be easily understood by a glance at the enlarged representations 

 (figs. 10 and \\\ wherein a portion of the spines have been purposely omitted, so as to show 

 the disposition of the pectinated expansions. The interior arrangements would appear to 

 be exactly similar to those we have already described in Athi/ris pectinifera, and, indeed 

 the two shells have been considered by several palaeontologists as belonging to a single 

 species. 



As we have fully described and represented the interior dispositions in the Permian 

 shell, and figured those also of another species of the same genus, A. ambigua, in PI. XVII 

 of the present monograph, it will not be necessary to repeat what has been already 

 written. 



In the limestone, on account of the hardness of the matrix, it is impossible to detach 

 the specimen with its outer spinulous surface, and for this reason the shell, in that con- 

 dition, was not recognised, and received from Professor Phillips the denomination of 

 Sp. glabristria, while to the specimens from the shales which retained their spinous ridges 

 the name of Sp.finibriata was applied : but both will require to be added to the synonyms 

 of L'Eveilles species, as well as that of A. depresm (M'Coy). Professor M'Coy observes, 

 at p. 433 of his Cambridge work, that "The equal, thick, longitudinal spines, which 

 fringe the narrow, concentric lamella? of shale specimens (of the species under description), 

 form an extremely marked character, and by their great strength and coarseness separate 

 the species certainly from the Devonian A. concentrica of V. Buch." In PI. XVIII. I 

 have represented the shell under various aspects, and to w.hich the reader is referred. 



Loc. A. Roumi is a common shell in the Carboniferous limestone and shales of mam 

 localities. In England it was found at Bolland, in the Isle of Man, at Ulverstone, and 



