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PROCEEDINGS OF THE ACADEMY OF [Vol. LXXIV 



of the comb-lateral are usually hidden by the overhanging mar- 

 ginals, even after the radula is flattened out. The centrals are 

 arranged in a slightly convex line along the bottom of the trough, 

 already mentioned, while the accessory plate is tilted slightly dor- 

 sad under the ends of the innermost marginals. 



The marginal group consists of a varying number (28 to 136 in 

 the species studied) of ligulate teeth. The number appears to vary 

 with the size of the species; but a considerable variation in number, 

 among species of similar size, appears to be a matter of systematic 

 importance. These teeth or uncini are proportionately quite large 

 and are so heavy as to appear horn-colored. They are arranged in 

 very oblique rows, which run posteriad from the corresponding 

 capituliform complex. The bases (Plate III, fig. 6, 9) are broadly 

 U-shaped, with the open portion of the U facing the outside of the 

 radula: those of contiguous teeth nest into one another. The 

 body of the tooth is twisted so as to bring the cusps into action. 

 These are arranged across the tip of the tooth or down its outer 

 side. The innermost marginal (Plate III, fig. 9) is the broadest 

 and shortest of the entire functional series. In the species observed 

 the length usually increases gradually toward the outside of the 

 radula, until the longest teeth are about one-third of the way 

 out from the center; here the teeth are from 1.5 to 2 times as long 

 as are the innermost. Towards the outer edge of the radula, 

 they again decrease in length, so that the outer teeth are not much 

 longer than the innermost. The distal portion becomes more 

 -lender in the teeth toward the outside, so that these may only be 

 one-third as wide, near the tip, as those at the inner edge. However, 

 the hases of the marginals are of about the same width throughout 

 each transverse row, andthevery outermost teeth take the form 

 of delicate, rectangular plates, as wide as the bases, and arranged 

 almosl parallel to the long axis of the radula. In all of the species 

 observed, the inner marginals (except sometimes the innermost 

 one or two) has the smallest number of cusps, while the number 

 gradually increases towards the outside of the radula. Each new 

 cusp in the series is added to the outside of the row of cusps. I 



ave as high as L5 cusps on the outer, definitive teeth, and have 

 mated, by counting portions of the total row, that some of the 



•road, outermosl marginals have at least 25. The cusps of these 



outer, scale-like teeth are so minute as to approach the limits of 



opic vision, which probably accounts for the statement 



