SCIENCE-GOSSIP. 



9 f 



os COLOUEING OF MOLLUSCS' SHELLS. 



v,\ Reginald J. 1 1 dghes. 



A\ inquirj into the colouring of molluscs' shells 

 may be arranged under three beads it ler 



to consider (1) the chemical composition of the 

 various pigments; (2) the object Eor which they 

 are deposited; and (3) the sourer from whence 

 they are derived. 



l. The mosl common colouring matter in British 



Fig. l. Typical Recent Shells. 



1. Venerupis enis (Med. Sea); 2. Helix pomatia (Italy); 

 :;. Cyclostoma plicata (Philippines); 4. Pythia leopardus (New 

 Caledonia); 5. Tapes decussata (Ajaccio) ; U. ETelicina major 

 (Cuba); 7. Cardium edule (Med. Sea); 8. Donax reticulata 



(CariliU'uii Seal: !>. Trm-ltim liinrob-ili (Adriatic); 10. Lucina 

 striatus (Italy); 11. Tellina nitida (Italy) ; 12. Same as 10, but 



a white example. 



Nip-. 5 and in coloured by iron, Nos. 2, 3, 7, and 8 by the first, 

 and remainder by second, form of organic pigment?. 



.•mil North European shells is sesquioxide of iron, the 

 tests lor which I have already described (SCIENCE- 

 GOSSIP, N.S., Vol. VI.. p. 241). This is found in all 

 British and many foreign bivalve genera, such as 

 Pecten, Ostrea, Mytilus, and Tapes, also in English 

 Ohitonidae, Naticidae, and Buccinidae. Mostofthe 

 above, it should be noticed, have a uniform tint 

 with little variegation. There is another very 

 common pigment, found in the shells of almost all 

 loiviv.li gasteropods, such as Aluricidae, Yolutidae, 

 ( lonidae, Cypraeidae, etc.. and some bivalves includ- 

 Lngthegenera Tridaena, Cardivm, and Donax (figA"), 

 Sept. 1900.— No. 76, Vol. VII. 



which is of an entirelj dill' rent nature and shows 

 no trace of iron, bu1 whose characteristic propert) 

 is thai of being turned violet-blue by pure nitric 

 acid. The colour, however, disappears when the 

 drop lit acid applied has dried. Ii is very soluble, 

 without change of tint, in hydrochloric acid, and 

 to a less extent in caustic potash or dilute nitric 

 acid. A number of tots have convinced me that it 

 eonl a ins no metal, but is of organic derivation, and 

 probably composed of the usual elements of such 

 I ii 'j i M ei its— viz. : carbon, hydrogen, and o: j gen. All 

 the brilliantly coloured tropical shells, with orna- 

 mental markings, have this pigment, except those of 

 the genera Turbo, Troelius, Solarium, Nerita, and the 

 bivalve genus Tellina (fig. 1). These are coloured 

 by a distinct form, also organic, that only differs 

 from the last in being unaffected in tint by nitric 

 acid, and is also less soluble. The two colouring 



Fig. 2. Eocene Si 



1. Volnta Uictatrix ; '.'. Lucina concenlrica; • 

 biffita; i. Cerithium concavum ; 5. Natica patula ; S, 

 serratum : 7. Waiicaparisit nsis; 8. Cardila imb icata; '■'. Chama 

 caltaraia, Nos. 7 and 9 (Paris basin) white; pigment i 

 :;, ." i Barton), and -' ( Paris basin) iron : remainder ( Paris basin) 



matters are most likely very closely allied; the 

 last-mentioned may even be the same as the first, 



with the addition of a mordant 'I he colour, on 



10 



