r 437 1 " ^'vM's\v\s\U>\fi. svO ')?.U 

 LXXII. Proceedings of Learned Societies. 



ROYAL SOCIETY, 



[Continued from p. 371.] 



March 23, 1854.— Colonel Sabine, R.A. and V.P., in the Chair. 



'T'HE following paper was read : — " Note on an indication of depth 

 -*- of Primaeval Seas, afforded by the remains of colour in Fossil 

 Testacea." By Edward Forbes, F.R.S., Pres. G.S. &c. 



When engaged in the investigation of the bathymetrieal distribu- 

 tion of existing mollusks, the author found that not only did the 

 colour of their shells cease to be strongly marked at considerable 

 depths, but also tliat well-defined patterns were, with very few and 

 slight exceptions, presented only by testacea inhabiting the littoral, 

 circumlittoral and median zones. In the Mediterranean only one in 

 eighteen of the shells taken from below 100 fathoms exhibited any 

 markings of colour, and even the few that did so, were questionable 

 inhabitants of those depths. Between 35 and 55 fathoms, the pro- 

 portion of marked to plain shells was rather less than one in three, 

 and between the sea-margin and 2 fathoms the striped or mottled 

 species exceeded one-half of the total number. 



In our own seas the author observes that testacea taken from below 

 100 fathoms, even when they were individuals of species vividly 

 striped or banded in shallower zones, are quite white or colourless. 

 Between 60 and 80 fathoms, striping and banding are rarely 

 presented by our shells, especially in the northern provinces ; 

 and from 50 fathoms shallow-wards, colours and patterns are well 

 marked. 



The relation of these arrangements of colour to the degrees of 

 light penetrating the different zones of depth, is a subject well worthy 

 of minute inquiry, and has not yet been investigated by natural phi- 

 losophers. 



The purpose in this brief notice is not, however, to pursue this 

 kind of research, but to put on record an application of our know- 

 ledge of the fact that vivid patterns are not presented by testacea 

 living below certain depths, to the indication of the depth, within 

 certain limits, of palaeozoic seas, through an examination of the 

 traces of colour afforded by fossil remains of testacea. 



Although their original colour is very rarely exhibited by fossil 

 shells, occasionally we meet with specimens in which, owing proba- 

 bly to organic differences in the minute structure of the coloured 

 and colourless portions of the shell, the pattern of the original paint- 

 ing is clearly distinguished from the ground tint. Not a few exam- 

 ples are found in Mesozoic as well as in Tertiary strata, but in all 

 the instances on record, the association of species, mostly closely allied 

 to existing tyjies, and the habits of the animals of the genera to 

 which they belong, are such as to prevent our having much difficulty 

 about ascertaining the probable bathymetrieal zone of the sea in 

 which they lived. 



