SCIENCE-GOSSIP. 



'45 



o\ COLOURING OF MOLLUSCS' .SHELLS. 



B\ Reginald J. 11 1 ghes. 



( Continued from pa te 99.) 



ET us now turn to fossil shells, and see how the 

 -- 1 — ' evidence they afford agrees with the deduc- 

 tions made from present-day forms. Little reliable 

 information can be gathered from shells of pre- 

 Eocene date. The colour is scarcely ever preserved, 

 being destroyed even if the shells are not altogether 

 petrified. I have, however, satisfied myself that 

 some bivalves from the chalk were coloured by 

 iron. There is also one Carboniferous species, 

 Pleurotomarid carinatd, belonging to the family 

 Trochidae, which deserves special mention. On it 

 the original wavy bands of colour are preserved, of 

 precisely the same type as found in Trochidae of 

 the present day. It is unlikely that a species 

 could alter its pigment without changing the 

 pattern of its coloration, so I may safely say, 

 although I have not myself examined a specimen, 

 that this shell was coloured by the organic and 

 rather insoluble pigment common on recent Tro- 

 chidae, thus showing this to be an extremely 

 ancient method of coloration. 



Among Eocene molluscs, all the terrestrial and 

 fresh-water shells from the London clay and else- 

 where which I have examined gave results similar 

 to equivalent shells of the present day. All were 

 coloured by an organic pigment, and that on 

 fluviatile genera, such as Planorbis, was unchanged 

 in colour by nitric acid. I need hardly say that in 

 testing fossil shells, especially marine species, 

 great care must be used to discriminate between 

 the original colour of the shell and subsequent 

 iron stains. Several examples of the same species 

 should be compared to ascertain what was the 

 original pattern, as on many specimens the mark- 

 ings are entirely destroyed. They should all, of 

 course, be first thoroughly cleaned, with dilute 

 hydrochloric acid if necessary. I have selected 

 the Barton clay for special examination, as the 

 shells from it are typical of the molluscan life in 

 England during this time, and are in a beautiful 

 stale of preservation. I can say with certainty 

 that the following were coloured with iron sesqui- 

 oxide (see fig. 2) : Crassxtella sulcata, Pectunoulus 

 deletus, Ostrea flabellula, Chama squamosa, Cardita 

 sulcata, Pleurotoma turdida, I', exarta, Dentalium 

 striatum, Phoms aggtutinans, Twritella edita, Eos* 

 tellaria awpla, Natica ambulacrum, N. patula, X. 

 depressa, Fusus pyrus, F. regularis. /•'. complicula- 

 tum, /'. longaevus, F. longorus, Seraphe fusiformis, 

 J/trrc.r eminent, Vohtta luctatrix I". ambigna, 

 and V. spinosa. Some seem to have been originally 

 white, as Bwceinum laxatum, Voluta sedbricula, 

 I. scalaris, )'. sub-ambigua, etc. Not one was 



coloured by an organic pigment, and Ml the 

 Volutes were marked by iron, although cvei 

 of that genus at the present time has an organic, 

 colouring matter. Most of these shells were 

 brown and had very little pattern, though some, 

 suchas Natica pal iila (fig. 2, No. ;"i).were beautifully 

 marbled, especially just inside the opening. Other 

 English formations of this period give similar 

 results. From the Bracklesham beds, Pecten 

 radiatus is one of the most interesting examples. It 

 was undoubtedly coloured by iron, thus agreeing 

 with recent Pectens. 



I woidd here call your readers' attention to the 

 physical geography of England at the time these 

 molluscs inhabited its waters. A great contineni 

 lay to the north and north-west of what is now 

 North-Western Europe, penetrated by a large gulf. 

 which opened into the sea to the south of the Paris 

 basin and extended inland as far as London. Into 

 this gulf one or more large rivers flowed, forming 

 extensive deltas and covering the sea-bed with 

 iron-impregnated mud derived from the erosion of 

 the surrounding country. On this deposit the 

 Volutes and other molluscs lived, in a tropical 

 climate, of which they themselves form part of 

 the evidence. Naturally their colour assimilated 

 to their surroundings, and for this purpose they 

 made use of iron, whose abundance an examina- 

 tion of any piece of Barton clay will demonstrate. 



In the Paris basin at the same lime we find a 

 very different state of things. The sea-bottom 

 here consisted either of limestone or light sands, 

 and accordingly many of the molluscs w< re white — 

 e.g. Cardium ohliqiuim, Cardita acuticos- 'ata, Litho- 

 oardiiimi aviculare, Fimbria lamellosa, Mosilia 

 sulcata, Cerithium cristatum, C'nudum, C.lapidum., 

 Natica par isiensis, N. sigarotina, and Fimts bulbu«. 

 Parts of the sea-bed were, however, covered with 

 sand not perfectly white, and parts in time becam • 

 again muddy, so often a certain amount 'if colouring 

 would be useful. And in this formation 1 haTefound 

 certain shells coloured by an organic pigment, 

 which is sometimes unaffected in tint by nitric 

 acid and sometimes turned light blue. As the 



colour, owing to its great age, is generall} fail t and 

 almost destroyed.it is probable that when living 

 blue would have been produced, in the majority of 

 instances. Of these shells Cardita imbricata was 

 rose-colour (fig. 2. No. s ) : Cerithium conravtnu 

 was white, with a series of orang round the 



shell, the projecting portions remaining white 

 (fig. 2. No. I): Cerithium sen-alum was salmon 

 (fig, 2. No. 6), and UosteUaria fissurella and 



