742 



The Living Animals of the World 



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

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

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

 posterior end of the back, while in others simjile 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-frerjuenting 

 species. ]!right scarlet, yellows, and blues, sejjarately or Aariously comliined, are among the 

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

 kind, having a flower-like dorsal gill-tuft, obser\ed 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, howe\'er, 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 tlie 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 tlie gills have a compactly disposed comb- 

 like contour. This gill-tuft is situated in an 

 excavated chamlier inside the shell, immediately 

 over the neck. Tlie Common Whelk, the 

 Pelican 's-FOOT Shkll, 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 conmron use obtained from such a 

 source include the ponderous Helmet-shells, or 

 CoNClis, employed for the manufacture of cameos ; 

 the Giant ^VHELKS and Trumpet-shells, often 

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

 '>at Polynesia and on the troijical Australian 

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

 and general dome.^ic receptacles throughout the same tropical area. To this list may be added 

 the Harp-siiells, ^ olutes, Cones, MiT.iES, 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 whic i the large, lioldly mottled "Tiger" and "Panther" species are well known 

 1 he comparatively small, yellowish, thickly built, porcelain-like shell of the " xMoney-COWRie " 

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



from ZT t r F ' T''"^''^' "' ''"^^ *°°' "^ *^^^^^ ^"^^1^ ^^"^11^' originally collected 



o n"n ''"■;'"■' \ "''^"'^ ^''""^ "^^ ^"'^^^^ l'«'-^ '^1«'- t° the African coast for 



de cl V t'V'l i' ""^ '"" ''"' '''''^' '^i""""^-'^ — -ie, pale pink in colour, with a 

 delicately streaked surlace, is indigenous to Britisli waters. 



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



fh',lo by W. Savilte-Ke.il, F.Z.S.] [ililford-on-Sca. 



HIGHLY I\IACXI1-IED TONGUE OF A SEA-SKAIL. 



With this stnictiire its owner bores or flies a hole tljroiiKh tlie shells 

 uf other Biolluscs ii]ion which it preys. 



