742 



The Living Animals of the World 



species occurring in British seas. They are notable for the slug-like form of their body, which 

 is usually supplemented by the outgrowth from it of complex, variously modified gill-filaments. 

 En some species these external gills take the form of symmetrical flower-like tufts at the 

 posterior end of the back, while in others simple or variously branched gills may be developed 

 on the upper-surface. The colours of many of these sea-slugs are more brilliant than those 

 of any other molluscs, this being especially the case with the tropical coral-reef-frequenting 

 species. Bright scarlet, yellows, and blues, separately or variously combined, are among the 

 dominant tints. Many of these tropical species are also of considerable size. One particular 

 kind, having a flower-like dorsal gill-tuft, observed by the writer on the West Australian 

 reefs, was over 10 inches long and 8 inches broad. Its general ground-colour was intense 

 vermilion, relieved, however, by a frilled border nearly an inch in width of the purest white, 

 with radiating streaks of scarlet. It is an interesting circumstance that these naked-gilled 



molluscs, shell-less so far as their adult phases 

 are concerned, emerge from the egg with a 

 perfectly formed, but necessarily very minute, 

 transparent shell, resembling that of a garden- 

 snail. It is consequently inferred that the group 

 has been derived from some permanently shell- 

 bearing form. 



The Comb-gilled section embraces the great 

 majority of the marine molluscs having a single 

 more or less convoluted or spirally twisted shell. 

 They take their name from the circumstance 

 that the gills have a compactly disposed comb- 

 like contour. This gill-tuft is situated in an 

 excavated chamber inside the shell, immediately 

 over the neck. The COMMON WHELK, the 

 PELICAN'S-FOOT SHELL, and the WINKLE are a 

 few typical British marine representatives of this 

 group, which, however, attains to the zenith of 

 its development in the size, variety of form, and 

 ornate coloration of its shells in tropical seas. 

 The inter-tropical coral-reefs in particular yield 

 a most abundant harvest in this direction. The 

 shells in common use obtained from such a 

 source include the ponderous HELMET-SHELLS, or 

 CONCHS, employed for the manufacture of cameos ; 

 the GIANT WHELKS and TRUMPET-SHELLS, often 

 over 18 inches long, used as signal-horns through- 

 out Polynesia and on the tropical Australian 



coast; and the capacious MELON-SHELLS, made to do duty for boat-baling and as water-vessels 

 and general domestic receptacles throughout the same tropical area. To this list may be added 

 the HARP-SHELLS, VOLUTES, CONES, MITRES, OLIVES, THORNY WOODCOCKS, and a host of others 

 prized by the conchologist. To this section must also be referred the innumerable species of 

 COWRIES, of which the large, boldly mottled " TIGER " and " PANTHER " species are well known. 

 The comparatively small, yellowish, thickly built, porcelain-like shell of the " MONEY-COWRIE " 

 constitutes, as is well known, the current coin throughout extensive areas of Africa and India. 

 It is recorded that as large a quantity as sixty tons of these small shells, originally collected 

 from tropical seas, have been shipped from one British port alone to the African coast for 

 commercial use within a single year. One very diminutive cowrie, pale pink in colour, with a 

 delicately streaked surface, is indigenous to British waters. 



The third large group of Molluscs which demands attention is that of the Bivalves, or 



Photo by W. Saviile-Kcnt, F.Z.S.] [Mil ford-on- Sea. 



HIGHLY MAGNIFIED TONGUE OP A SEA-SNAIL. 



With this structure its owner bores or files a hole through the shells 

 of other molluscs upon which it preys. 



