New Zealand Tertiary Rissoids. By H. J. Finlay, M.Sc., Edmond Fellow of Otago University. [Read before the Otago Institute, 12th December, 1922; received by Editor, 31st December, 1923; issued separately, 30th July, 1924.] Rissoids are not usually plentiful as fossils in New Zealand. In the latest list of our Tertiary Mollusca (Suter, 1918) nine species of Rissoa and Rissoina are recorded; five of these are also Recent species, and only one of the other four is from the Miocene. In the present paper the number of Rissoids recorded as fossil from New Zealand is raised to twenty-five, fifteen of these being described as new, most of them being from Miocene beds. Hutton (1873, 1885, 1893) was the first to describe members of this family from the New Zealand Tertiary; five of the nine species above mentioned were originally described from the Pliocene beds of Petane or Castlecliff, one from Awamoa (Miocene), and the remaining three were discovered fossil subsequent to their description as Recent species. The only addition made to this number in recent years is Rissoina (?) obliquecostata M. & M., described by Marshall and Murdoch (1920A) from Hampden. Although these small shells are termed Rissoids, Iredale (1915) has shown that the type name, Rissoa, should not be applied to any Neozelanic shells, and has provided a series of generic names to cover austral forms. His scheme marks a decided advance in their treatment, and by it New Zealand Recent Rissoids can be reduced to some semblance of order. Strong support for his action is given by the ease with which practically all the fossil Rissoids so far discovered fall into his groups. Iredale might, however, have been more generally explicit in defining his genera. It may be legally correct to define a new genus—e.g., Merelina—by “proposing it for shells grouped around Rissoa cheilostoma Ten.-Woods,” but this is extremely unsatisfactory for workers who have not access to large suites of actual specimens, and have to rely mostly on literature. To ensure immediate appreciation and acceptance of new genera a résume of diagnostic characters is imperative. From Iredale's treatment of the Rissoids it was almost inevitable that when his names did come into use some of them should be misapplied, and this has already occurred. The genus Estea, in particular, seems to have given trouble—the writer has seen one of the spirally lirate species determined as a Subonoba; and, further, Marshall and Murdoch (1920B) have listed Rissoa semisculcata Hutt. as a Lironoba, to which genus it bears little resemblance. As far as the writer can see, the following diagnostic notes (compiled after study of New Zealand Recent and fossil species) represent Iredale's ideas fairly correctly; he would, however, have saved Neozelanic workers much trouble had he given a similar table when his genera were proposed.