Members of this family are shaped rather like bonnets or helmets, as their common name suggests. The shells are large, thick, subglobular with dextrally coiled, sometimes varicose, whorls, and a short spire. The coiling may be trochospiral or convoluted.

The shells of many species have great variability, which has led to many misidentifications, resulting in many synonyms. Many species have a large and solid shield over the parietal body or beside the thick, plicated columella. Many species show blunt knobs and thickened axial ridges, known as varices. The thin, horny operculum is oval in shape and covers a long aperture. The siphonal canal is straight or slightly curved. The outer lip is somewhat thicker at its margin and toothed on the inside.

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Casmaria erinaceus (Common bonnet)
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Casmaria erinaceus (Common bonnet)

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Cassis cornuta (Horned helmet)
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Cassis cornuta (Horned helmet)

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Cassis fimbriata (Fimbriate Helmet)
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Cassis fimbriata (Fimbriate Helmet)

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Cassis madagascariensis (Queen helmet)
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Cassis madagascariensis (Queen helmet)

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Cassis nana (Dwarf Helmet)
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Cassis nana (Dwarf Helmet)

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Cassis tessellata (West African helmet)
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Cassis tessellata (West African helmet)

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Cassis tuberosa (King helmet)
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Cassis tuberosa (King helmet)

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Cypraecassis rufa (Bullmouth helmetshell)
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Cypraecassis rufa (Bullmouth helmetshell)

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Cypraecassis tenuis (Galapagos cowrie-helmet)
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Cypraecassis tenuis (Galapagos cowrie-helmet)

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Cypraeacassis testiculus testiculus (Reticulated cowrie-helmet)
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Cypraeacassis testiculus testiculus (Reticulated cowrie-helmet)

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Cypraecassis testiculus senegalica (Senegal cowrie helmet)
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Cypraecassis testiculus senegalica (Senegal cowrie helmet)

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Echinophoria carnosa (Chalky Bonnet)
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Echinophoria carnosa (Chalky Bonnet)

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Echinophoria kurodai (Kuroda's Bonnet)
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Echinophoria kurodai (Kuroda's Bonnet)

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Echinophoria wyvillei (Wyville's bonnet)
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Echinophoria wyvillei (Wyville's bonnet)

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Galeodea echinophora (Mediterranean Spiny Bonnet)
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Galeodea echinophora (Mediterranean Spiny Bonnet)

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Galeodea keyteri
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Galeodea keyteri

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Galeodea rugosa (Rugose bonnet)
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Galeodea rugosa (Rugose bonnet)

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Galeodea nipponica
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Galeodea nipponica

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Phalium areola (Checkerboard bonnet)
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Phalium areola (Checkerboard bonnet)

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Phalium areola f. magnita
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Phalium areola f. magnita

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Phalium bandatum (Banded bonnet)
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Phalium bandatum (Banded bonnet)

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Phalium fimbria (Fimbriate Bonnet)
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Phalium fimbria (Fimbriate Bonnet)

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Phalium flammiferum (Striped bonnet)
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Phalium flammiferum (Striped bonnet)

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Phalium glaucum (Gray bonnet)
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Phalium glaucum (Gray bonnet)

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Phalium muangmani
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Phalium muangmani

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Phalium pseudobandatum
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Phalium pseudobandatum

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Sconsia grayi (Royal bonnet)
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Sconsia grayi (Royal bonnet)

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Semicassis bisulcata (Japanese bonnet)
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Semicassis bisulcata (Japanese bonnet)

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Semicassis canaliculata (Channeled Bonnet)
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Semicassis canaliculata (Channeled Bonnet)

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Semicassis glabrata (Smooth Bonnet)
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Semicassis glabrata (Smooth Bonnet)

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Semicassis labiata f. iredalei (Iredale's Bonnet)
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Semicassis labiata f. iredalei (Iredale's Bonnet)

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Semicassis pyrum (Pear bonnet)
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Semicassis pyrum (Pear bonnet)

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Semicassis saburon (Saburon Bonnet)
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Semicassis saburon (Saburon Bonnet)

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Semicassis thomsoni (Thomson's bonnet)
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Semicassis thomsoni (Thomson's bonnet)

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Semicassis undulata (Mediterranean Bonnet)
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Semicassis undulata (Mediterranean Bonnet)

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