364 



fig. 604, p. 859) regards the large plate to which the marginals 

 are joined as an extra tooth. 



Emarginula dilecta, A. Adams. 

 PL xix., No. 10, x 300. 

 Dental formula * • 1( Y 8 4)lQC . Radula delicate, bilaterally 

 asymmetrical. Middle tooth of centrals, broad; the outer- 

 most with two flanges, one overlaping the next inner tooth, 

 the other extending behind the lateral. All the centrals have 

 a very fine serrated edge like the teeth of a saw. The single 

 lateral large and bicuspid. Marginals, in two parallel rows 

 of seven each, with their bases attached to the outer side of a 

 small plate, parallel to the length of the radula. 



Phasianella australis, Gmelin. 

 PL xix., Nos. 5a and 56, x 150. 



Dental formula x ' 38 °' — . Radula very coarse, dark-red; 

 details hard to see owing to its opacity. Central tooth narrow 

 and inconspicuous. Five laterals rectangular, with a single 

 blunt cusp; the three outer with a distinct flange lying behind 

 the next inner tooth. Marginals with one remarkably devel- 

 oped cusp almost as large as their bases. The first marginal 

 differs slightly from the rest in having its cusp smaller, with 

 a second blunt one at its base, which fits into a socket in the 

 second marginal. This second marginal has two of these small 

 blunt cusps, and as the marginals diminish in size the number 

 of these cusps increases till there are four or five, and at last 

 are as large as the primary cusp which has gradually decreased. 

 A separate figure (pi. xix., No. 5r/ ) is given of the first three 

 marginals, to show the intricate manner in which they 

 interlock. 



Phasianotrochus irisodontes, Quoy and Gaimard. 

 PL xix., No. 6, x 200. 



Dental formula x • U5 ^ 5U - QC . Of the central teeth the 

 middle one is peculiar- in having a double flange at its base, 

 and two small cusps on each side of the large cusp, which is 

 broad and rounded at the end. The five adjoining central 

 teeth have a large cusp with the two small cusps only on the 

 side further from the middle tooth, and have a single flange 

 on the outer side of the basal plate in front of the plate 

 outside it. The single lateral is dwarfed in size and rudi- 

 mentary in shape. The marginals have one cusp with a very 

 fine serrated edge, and a long narrow base. They gradually ~ 

 decrease in size, and are very numerous. 



