The Cambridge natural history . (JVeritojJsis) only three. Thelateral next to the uncini (which is specially large in theNeritidae, and is then known as the capituliform tooth) isregarded by some authorities as the first nncinus, by others asthe sole representative of the laterals, the teeth on the innerside of it being reckoned as multiplied central teeth. Accord-ing to this latter view, Livoiia will have as many as seventeencentral teeth. Taking five as the average number of laterals,we shall have the following different ways of constituting therhipidoglos-sate formula, the first being that
The Cambridge natural history . (JVeritojJsis) only three. Thelateral next to the uncini (which is specially large in theNeritidae, and is then known as the capituliform tooth) isregarded by some authorities as the first nncinus, by others asthe sole representative of the laterals, the teeth on the innerside of it being reckoned as multiplied central teeth. Accord-ing to this latter view, Livoiia will have as many as seventeencentral teeth. Taking five as the average number of laterals,we shall have the following different ways of constituting therhipidoglos-sate formula, the first being that to which preferenceis given, viz. :— (1) , one central, five laterals, includingthe last lateral tooth. (2) ( ).( ), regarding the last lateral as first uncinus, but specialising it by a number. (3) cc. 1.(). , regarding the last lateral as the onlylateral. In the Neritidae and the derived fresh-water genera {Neritina,Navicella) the first lateral, as w^ell as the capituliform tooth, is. Fig. ]30. —Portion of the radiila oi Nerita albicillu, L., Andaman Is., with ctntral toothhighly magnitied : c, c, the capitnliform tooth. x 40. very large, and in shape rather like the blade lione of a shoulderof mutton ; the intervening laterals are very small. InNeritopsis (a degraded form) the central tooth and first lateralare entirely wanting. In the neritiform land-shells {Helicina,Proserpina) the first lateral is no larger than the others, whilethe capituliform tooth is enormous. Hydrocena is a veryaberrant and apparently degraded form; the laterals between thefirst and the capituliform tooth are all wanting. In Haliotis,Scissurella, and Fleurotomnria the five laterals are of fairly equal OF THE DOCOGLOSSA 227 size; in Fissnrella we again meet with a large capitulifornitooth, with very small laterals. (g) The Docoglossci are in direct contrast with the Ehipido-glossa in possessing few and strong teeth, instead of many andweak. There ar
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
