12 



PRO< EEDINGS OF THE ACADEMY OF [Vol. LXXIV 



ate basally. As remarked in the key to the groups, the cusps of the 

 paired centrals, and especially those of the C-central, are larger 

 and better-developed than in any other group; in fact the whole 

 central group is large in comparison with the rest of the radula. 

 The comb-lateral has comparatively few cusps, but these are large, 

 and exceptionally long and well-pointed (Plate IV, fig. 10). The 

 accessory plate is heavy bu1 short, and has horn-colored thickenings 

 along the inner end and down the middle, while in most of the 

 nearly related groups it is comparatively transparent. The re- 

 flected wing is large and triangular, although much shorter (trans- 

 versely) than in Oligyra. The marginals are practically the same 

 shape as those of 0. orbiculata. All are evenly ligulate, with a 

 decided tendency for the cusps to be arranged on the outside of 

 the tips. 



The radula of H. japonica is not figured as it is practically 

 identical with that of H. occulta. One more cusp on the B-central 

 was noted in one radula of H. japonica but it was absent in the 

 other radula examined. This species also showed a slight tendency 

 to increase the number of cusps on the marginals more rapidly 

 than did //. occulta (see Table II). This practical identity of the 

 radulae, despite the divergence in opercula, is the reason for the 

 inclusion of Waldemaria as a section in the genus Hendersonia. 

 I am very doubtful if Miluna even deserves sectional rank, but 

 have seen no specimens. 



Table II. Radular Formulae in Hendersonia and Oligyra. 



Centrals Comb Marginals Grand 



A H C Lateral 2 3 4 5 6 Total Total. 



II- occulta 5 5 4 6 7 5 5 5 39-40 89-91 



H. japonic 5 5-6 4 6 5 7 5 5 42-43 95-97 



A.verecunda 7 8 4 10-11 1* 2+3 4 3 50 111 



0. orbiculata 4 6 4 6 3 4 10 7 52 115 



O.convexa 4 6 4 7 1* 2+3 2 2 4 81 173 



O.f.strebeli 5 8-9 4 7 3 4 3 3 58-62 127-134 



O.o.coccinostoma.... 4 7 4 7 5 3 3 3 90 191 



0. cacaguelita 2? 4 4 7 4 6 2 4 95 201 



O.riparia 5 5 4 9-10 7 6 5 73 157 



0. rotunda. 4 5 4 7 1 10 7 82 175 



O.palliata 5 5 4 8 10 5 4 5 123 257 



rhe radula of Hendersonia is very close to that of Oligyra, and 



the separation of the two, on this basis alone, might be rather 



However, the shell-characters of Hendersonia^ its wide 



tion, and its significance as a primitive, holarctic group 



