IndusUnal and Mamifacturing Uses of Shells. 303 



nucleus is then very eccentric. The spirals are invariably 

 sinistral in dextral shells. Horny operculum — Biicciniim 

 undatiim; calcareous — TrocJms and Triton, Turbo sarmaticus, 

 T. marmoratiis, nodostis, Cookii, and torqicatics. Some of these 

 coloured solid opercula have recently been polished and 

 set as ornaments of jewellery for necklets and pins, studs 

 and solitaires. 



The opercula of the screw or stromb shell, and some 

 other species, were formerly officinal under the name of 

 Unguis odoratiis or Blatta hyzantina. Small horny opercula, 

 called Sheitam temah, are still used medicinally on the coast 

 of Syria. The operculum of the whirl-wreath or Turbo 

 cochins and other species form the tmtbilicns veneris. 



Dyes from Mollusca. — Formerly some valuable dyes 

 were obtained from molluscs, of which sepia and the ancient 

 Tyrian purple dye are examples ; but the abundance of 

 mineral, insect, and vegetable dyes now available renders 

 these valueless at present. Still a notice of them is worth 

 attention. 



The colour known as sepia among artists is a liquor 

 contained in the ink-bag of Sepia officinalis. It is of a 

 powerful dusky-brown colour, and works admirably in 

 water, being used in making drawings in the manner 

 of bistre and Indian ink, but is not applicable with oil. 

 This warm and sober colour has not, up to the present, 

 been employed in the photographic impressions called " the 

 carbon " process. Sepia is sold in little bladders, which 

 have to be freed from membranes. This is very easily done 

 by boiling it for a moment in chloric acid, which destroys 

 the envelope, and causes it to become detached by tritura- 

 tion with the hands in water. The bag or pocket, being 

 light, floats and is easily separated by filtering. The black 

 substance which remains is dried, after having been washed 

 in hot water. 



