RIIIPIDOGLOSSATE TEETH. 
2CA 
ill 38 transverse rows, each with a trifidly reflected median tooth, 
flanked on either side by two lateral teeth with three cusps, and by 
ten or more aculeate marginal teeth, the innermost having two cutting 
points and being transitional in character. 
The Cl.\ssification of the odontophores of our native species is a 
task of considerable difficulty, but their study at once suggests the 
desirability of separately considering and grouping the Streptoneurous 
and Euthyneurous forms. 
The Streptoneura have long been known to possess such very 
persistent and characteristically varied types of teeth that their 
peculiarities have, by almost universal consent, been utilized as a 
basis for forming natural groupings of this section of the mollusca. 
Our Streptoneurous species may all be placed under the two well- 
known groups, Ilhipidoglossa and Tsenioglossa. 
The Rhipidoglossa {piirk, fan ; yA.wcrcra, tongue) are especially 
characterized by the extraordinary number and marlved uniformity 
of the uncini or marginal teeth, which are usually very compactly 
arranged in a somewhat curvilinear or fan-like manner, diminishing 
gradually in size as they approach the outer margins of the radula. 
Fig. 531 Transverse row of teeth from the odontophore of Ncritina Jhiviatilis (L.), highly 
magnified. River Nene, Northampton, collected by Mr. L. E, Adams, B.A., and prepared by 
Mr. J. W. Neville. 
In Neritina fluv'mfiUs, our only representative of this group, the 
central teeth are obscurely trifid, the laterals of very dissimilar size 
and shape, with the flrst and the outermost of the scries exceptionally 
