100 



SUPPLEMENT TO THE 



The Rev. Norman Glass and myself are of opinion that in some of the species of 

 Athi/ris the loop and attachments, whilst on the whole similar to those of A. plano- 

 sulcata, are slightly modified in minor details ; such modifications, so far as our present 

 knowledge extends, being confined to some of the species in the Devonian rocks of 

 America. Por example, in A. spiriferoides (a shell much resembling in shape and size 

 the Athyris concentrica of von Buch, and extremely abundant in the Hamilton Devonian 

 group at Eighteen-Mile Creek, Lake Erie, and in other places in America), the part of 

 the primary lamella where the curve of the first coil of the spiral commences is not 

 widened as in A.plano-sulcata ; and the attachment to the hinge-plate lies more backward 

 towards the dorsal side, and does not appear, as in A. plano-suhata, in the ventral aspect 

 of the spirals. In the figure of A. spiriferoides given by Professor Hall in vol. iv, p. 

 284, of his work on the ' Palaeontology of New York,' the attachment to the hinge-plate 

 is represented as forming, together with the commencement of the curve of the first coil of 

 the spiral, a perfect circle. Mr. Glass found, however, in some specimens of this species 

 which he worked out, that the attachment to the hinge-plate, together with the commence- 

 ment of the curve of the first coil of the spiral, forms a somewhat elongated oval, which is 

 slightly angular at its lower part. The loop in A. spiriferoides, as given by Professor 

 Hall, differs from that worked out in the same species by 

 Mr. Glass, and this is found to be similar to that of A. 

 plano-sulcaia, only differing from it, indeed, in the shape 

 and size of the roof-shaped projection in the centre. 

 Professor Hall represents the supplementary lamella of A. 

 spiriferoides as being attached to the primary lamellae. 

 Mr. Glass found, it is true, in some specimens the sup- 

 plementary lamellae were in close apposition to the primary 

 lamellae, as he had also found to be the case in many speci- 

 mens of A. plano-sulcata ; but in one specimen of A. spiri- 

 feroides Mr. Glass discovered the ends of the supplementary 

 lamellae to be free. 



Mr. Whitfield has recently informed Mr. Glass that 

 in the American Devonian species of Athyris the ends 

 of the supplementary lamellae are free. Professor Hall 

 figured, together with A. spiriferoides, the loop and 

 attachments of A. vittata, and the internal arrangements 

 of the two species are represented as being very similar. 

 Mr. Whitfield, with the greatest kindness, lent me some 

 of the preparations from which the original figures 

 o[A. spiriferoides and A. vittata were taken, but neither llw Glass nor myself could deter- 

 mine anything from them. Mr. Whitfield also furnished my friend with a number of 

 unworked specimens of A. spiriferoides, but he could not supply him with any duplicate 



1, 2, 3, Athyris spiriferoides. 

 1. Showing sjiirals, loop, and attach- 

 ments to hiiigo-plate. 2, 3, the loop, 

 attachments to the hinge-plate, &e. 

 Enlarged. Developed by the Rev. N. 

 Glass. 



