The royal natural history . ce, it isthickened with an outer shelly layer, consists of fewer whorls, and often has thenucleus excentric. The latter family is typified by the genus Turbo, which has beendivided into a number of groups or subgenera on account of differences in thisstructure. The species are fairly numerous in tropical seas, but rare in more tem-perate regions. Of the allied genus Phasiandla only one species (P. pullus) reachesthe British shores. The Trochida have a wider range, are far more numerous, andoccur everywhere from the Arctic to the Antarctic circles. The beauty of scul
The royal natural history . ce, it isthickened with an outer shelly layer, consists of fewer whorls, and often has thenucleus excentric. The latter family is typified by the genus Turbo, which has beendivided into a number of groups or subgenera on account of differences in thisstructure. The species are fairly numerous in tropical seas, but rare in more tem-perate regions. Of the allied genus Phasiandla only one species (P. pullus) reachesthe British shores. The Trochida have a wider range, are far more numerous, andoccur everywhere from the Arctic to the Antarctic circles. The beauty of sculptureand coloration of many of the species of the typical genus Trochus is beyond descrip-tion, and can only be appreciated by an examination of the shells themselves. Mostforms are littoral, or inhabitants of shallow water, but a few, and these among themost beautiful, have been dredged at enormous depths. Nearly twenty differentspecies occur around the British coast, and some of them are extremely elegant in 396 form and structure. The family Delphinulidce in many respects resembles theTrochidce, and is represented only by the single tropical genus Delphinula. Theormers (Haliotidce), although few in number, form an important family, on accountof the economic value of the beautiful pearly shells which are employed in are ear-shaped, depressed, with a very small spire, and the last whorl, whichpractically contains the entire animal, correspondingly large, and pierced with aseries of holes commencing at the spire and extending to the front margin, in aline subparallel with the left side. The outer surface is calcareous, and oftenbeautifully sculptured and coloured, but the interior is lined with the mostbrilliant pearl. The holes in the shell admit water to the gills through a slit in the mantle beneath, and on the edges of the slit there are three tentacularprocesses which the animal passesthrough certain perforations. Hal-iotis, like the limpets, has a
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
