On the Form, Growth, and Construction of Shells. 247 



which enables it to resist the summer drought, and exclude all 

 enemies. • 



4 



FlG. 5. Cargchium minimum, highly magnified. FlG. G. Cgelostoma elegans. 



In the Coloured Plate, at Fig. 3, is represented a specimen 

 of the foreign land- snail, Tropidophora carinata, presented to 

 the author by that indefatigable traveller, the late Madame Ida 

 Pfeiffer, which was brought alive by her with other specimens 

 from the Mauritius. It was perfectly lively and well after six 

 months' close confinement, wrapped up in an old sock in a tin 

 pot. 



The periwinkle has a similar operculum, of a horny con- 

 sistency and spiral structure ; but the exotic Turbos have a 

 solid, shelly operculum (see Plate, p. 245, Pigs. 1 — 3), coated 

 inside with rich brown, and spirally marked with Hues of 

 successive growth ; while the exterior is smooth, or corrugated, 

 like the tufa of a dripping well (same Plate, Pig. 3, h), or 

 variously carved. 



In the great pearly Turbo marmoreus, so often used for a 

 sideboard or mantelpiece ornament, the operculum frequently 

 weighs several ounces. A specimen in the shell- gallery of the 

 British Museum weighs more than half a pound. 



The whelks and all their tribe have horny opercula, and the 

 pattern is often characteristic of the genus ; the operculum of 



M 



Fig. 7. The Dog-whelk, Ffassa EiG. 8. The Dog-whelk, Purpura lapilhis, 



reticulata. and a small cluster of its egg-capsules. 



the whelk is never spiral. (See Woodcut, Fig 9.) Gregarious 

 animals, such as the whelk and periwinkle exhibit malforma- 

 tions more frequently than others ; thus we have whelks with 

 double opercula, others with shells repaired after injury or curi- 

 ously contorted. Mr. W. H. Eich, of No. 14, Great Russell 

 street, Bloomsbury, W.C., has devoted much time to the 

 collection of anomalous forms of British shells. He will be 



