274 Zoological Proceedings of Societies. 



Lias, all the fossils may be referred to some of those orders. In 

 the Tertiary beds, the approximation is progressively extended, 

 and the shells of the London Clay may all be referred to some 

 existing Genus; but no fossil can be completely identified with 

 any living Species, except in those uppermost beds, which lie 

 between the London Clay and our present creation. Mr. Dillwyn 

 likewise gives some further observations on the changes which 

 took place when the Chalk deposits were completed, and addi- 

 tional reasons for believing that the Mollusca in our latitudes then 

 required a more perfect protection, either from their enemies, or 

 from the surrounding elements, than afterwards became neces- 

 sary. He also notes the exceptions to the inference in his former 

 paper respecting the Aporrhaides', and other fossil Trachelipodes', 

 occurring in secondary formations, feeding only on dead animals, 

 which are afforded by the perforated shells in the denuded 

 tracts of Green Sand in Devonshire ; and alleges some reasons 

 for suspecting that a mixture of strata may have occurred at 

 the time when those denudations took place. 



April 1. — The reading was commenced of An Inquiry re- 

 specting the nature of the luminous power of some of the 

 Lampyrides ; particularly of L. splendidula, L. Italica, and 

 L. noctiluca ; by Tweedie John Todd, M.D. : communicated 

 by Sir E. Home, Bart. V.P.R.S. 



April 8. — The reading of Dr. Todd's Inquiry was resumed 

 and concluded. It commences with some general remarks on 

 the various causes to which the luminosity of the Lampyrides 

 has been ascribed ; the explanation of Macartney and Macaire, 

 that the light they emit is a simple product of vitality being 

 considered as the true one. Dr. Todd then proceeds to a mi- 

 nute account of the apparent source and characters of the light 

 in the several animals ; describing the manner in which its 

 emission is affected by solar and other light, by heat, and by cer- 

 tain chemical agents respectively. In the Lampyris splendidula, 

 the light is of a fine topaz-yellow colour, with a tinge of green, 

 and is extremely vivid within the compass of a few inches, but 

 does not extend its brilliancy far around ; within that space the 

 hour may be seen on a watch by its means. The light of the 



