RADULA OF THE RACHIGLOSSA 



221 



group are the possession of a central tooth with from one cusp 

 (^Boreofusus) to about fourteen (^Bullia), and a single lateral more 

 or less cuspidate, the 

 outer cusp of all being 

 generally much the larg- 

 est. Thus in Melonge7ia 

 respertilio (Fig. 117) the 

 central tooth is tri- 

 cuspid, the central cusp 

 being the smallest, while 

 the laterals are bicuspid ; 

 in Ehurnajaponica (Fig. 



118) the central tooth is 5-cusped, the two outer cusps being much 

 the smallest. The teeth, on the whole, are sharp and hooked. 



Fig. 120 



— Portion of the radula of Imbricaria 



laannorata Swains, x 80. 



Fig. 121.— Three rows 

 of teeth from the 

 radula of Fasciola- 

 ria trapezium Lam. 

 X40. 



with a broad base and formidable cutting edge. In the Olividae, 

 Turricula^ Buccinopsis^ and the Muricidae the laterals are unicus- 

 pid and somewhat degraded (Fig. 119). In 

 Mitra and the Fasciolariidae they are very 

 broad and finely equally toothed like a comb 

 (Figs. 120, 121). The whole group is desti- 

 tute of marginals. 



Several remarkable peculiarities occur. 

 Harpa loses the radula altogether in the adult. 

 In the young it has lost only the laterals, 

 and consists of nothing but the central tooth. 

 Marginella has no laterals ; the central tooth 

 is small and comb-shaped, with blunt cusps. 

 In Valuta the laterals are generally lost, but 

 in Volutomitra and one species of Voluta ^ they 

 The central tooth usually has three strong cusps. 



Fig. 122.-^ Six teeth 

 from the radula of 

 Cymhium diadema 

 Lam., Torres Strait. 

 x25. 



are retained. 



^F. concinna, according to Schacko (Conch. Mitth. i. p. 126, PI. xxiv. f. 5); the 

 lateral is large, strong, unicuspid on a broad base. 



