The Cambridge natural history . )oda, {h) to the dilfcrs, however, morphologically from the former in tiieessential ])oint of not being produced l)y the mantle, and fromthe latter in not lieing produced l)y a special gland. As regards shape and formation, the operculum has usuallya more or less well-marked nucleus which may be central (), subcentral (Anqmllaria), lateral (^JKijrura), or terminal. Turbo(Sanuaticus) Livoiia Tiulio(Callopoiiia) Fig. 182.—Various forms of open-ula Anipnllaria Xatiea (Fijoida). As a rule, l)oth the inner and outer surfaces are fairlyflat, but in
The Cambridge natural history . )oda, {h) to the dilfcrs, however, morphologically from the former in tiieessential ])oint of not being produced l)y the mantle, and fromthe latter in not lieing produced l)y a special gland. As regards shape and formation, the operculum has usuallya more or less well-marked nucleus which may be central (), subcentral (Anqmllaria), lateral (^JKijrura), or terminal. Turbo(Sanuaticus) Livoiia Tiulio(Callopoiiia) Fig. 182.—Various forms of open-ula Anipnllaria Xatiea (Fijoida). As a rule, l)oth the inner and outer surfaces are fairlyflat, but in Torinia, Cyatho2-)oma, and Ftcrocyclus the outer sur-face is elevated and conically spiral, in some Turho ( Sarmati-ciis) it is covered with raised tubercles reseml)ling coral, while inothers ( Callopoma) it is scored with a deep trench. Aalo-2wma, a land genus peculiar to Ceylon, has a paucispiral oper-culum with hollow whorls, deceptively like a PlanorUs; it fitsover the aperture instead of into it. In Livona and mostTrochidae the operculum is cartilaginous and multispiral. InStromhus it is narrow, curved, and often serrated like a leafon one of the edges; in Conus it is narrowly oblong and ratherfeatureless; in Littorina, paucispiral and always cartilaginous. ^ .T. E. Gray, ridl. Trans. 1833, p. 812. PARTS OF THE SHELL IN BIVALVES 269 111 many cases ( Taludina) there is no true syjiral form
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
