222 PROCEKDINGS OF THE MALACOLOGICAL SOCIETY. 1 



semilunar, horny, concentric, with a lateral nucleus: inner edp;e' 

 thickened, with an internal rib from the nucleus, but no projecting rib. 



Type, Heterorissoa secimda, Ii'edale. 



This genus apparently takes the ])lace of Jeffreysia in the Southern 

 Hemisphere ; in sliell characters it agrees A-ery closely with thati 



genus, but the operculuiu differs in lacking the projecting rib. Tlie 

 shell recently described as J. Wilfridi (Gatliff & Gabriel, Proc. Hoy. 

 Soc. Vict., vol. xxiv, p. 188, pi. xlvi, fig. 3, 1911) I would consider 

 to belong to my genus, also J. Edivardiensis, Watson (Cliall. Rep. 

 Zool., vol. XV, p. 584, pi. xliii, fig. 5, 1886), from Prince Edward 

 Island. 



Thais, Bolten. 



In this Journal, vol. ix, p. 322, 1911, I indicated my interest in 

 the generic treatment of the molluscs formerly chassed undQY Purpura, 

 liruguiere, but now known by the name of Thaia, Bolten. At that 

 time I was unaware that the group had been recently discussed bj^ 

 Dall (Dep. Int. U.S. Geol. Surv., Prof. Paper No. 59, 1909), and it 

 was therefore with much interest that I studied his results. I hope 

 to more fully deal with the conclusions there arrived at, but would 

 here give expression to some points whereon I consider amendment 

 possible. Before proceeding further I would express my deep 

 gratitude for the great work which Dr. Dall is still doing ; putting 

 on record valuable synthetic ]iapers, whereby analysis is made 

 possible to those who are not skilled in the more difficult task of 

 synthesis. 



I have already definitely concluded that the juvenile stages of 

 molluscs must be studied before generic groups can be considered 

 stable. Though Dall has studied the animals, and found little 

 variation, I do not find in his paper anj" notice having been taken 

 of the earlier stages, and consequently in his treatment of the 

 New Zealand and Australian Tliaitids I find disagreement with my 

 own studies. 



Dall recognizes Lepsia, Hutton, proposed for Purpura haustrum, 

 Martyn, as of sectional value, under the sub-genus Thais. The method 

 of classing the Thaitids, as one genus only, I consider improper, and 

 the four sub-genera seem absolutely artificial. The skeletal nature 

 of Dall's system is most perplexing to the Austral student who finds 

 no place for his most coraihou friends. For instance, take the group 



