Perhaps chione will find a home under Megapitaria Grant and Gale as a subgenus of Costacallista. No specimens of the genotype, Cytherea aurantiaca Sowby., were available to the writer for comparison, but Gray's figure of his species, squalidus, which Grant and Gale included in Megapitaria, shows a shell very like chione.

Grant and Gale (1931, p. 346) have solved the difficulty of choosing between Macrocallista, Megapitaria, Amiantis, Hysteroconcha and Pitar as genera by suggesting that Pitar, the oldest name, should be taken as a genus and all the other groups with this general type of hinge included as equivalent subgenera. This seems to be the only good alternative to recognising these and such other groups as Chionella, Calipitaria, Tivelina, Costacallista and Notocallista as independent genera. Each course has its advantages; but as our knowledge of the many lineages increases, the tendency will be to elevate all those mentioned and others to generic rank. As noted by Stewart, the use of sectional subdivisions of subgenera is rather clumsy for citation and is not sanctioned by the International Rules; consequently, the best plan seems to be greatly to restrict the older, wide, “Lamarckian” genera and to use genera of intermediate size with only subgeneric divisions. From this point of view, the best classification for chione Linné appears to be under Costacallista (Megapitaria).

Australian and New Zealand shells at present classed as Notocallista fall into three main groups which can be treated as subgenera under the genus Notocallista. These subgenera, Notocallista s. str. Striacallista and Fossacallista, typically are easily separable, but their respective limits are difficult to define because of borderline species that combine characters of two groups. Although this is a source of difficulty in drawing up a concise key to the species, it should not act as a barrier to the recognition of systematic groups. The three here recognised are of somewhat unequal value, for Fossacallista is much easier to separate from Notocallista than is Striacallista.

According to the evidence so far gained, Fossacallista is probably the oldest group, being related to the European Chionella, which has in its juvenile stage similar fine concentric ridges. Fossacallista lived in Australian and New Zealand seas during the Oligocene and Miocene, but became extinct in both regions before the Pliocene. Striacallista probably developed from Fossacallista in Australia during the Oligocene (N. cudmorei n.sp.), but it did not reach. New Zealand until the Lower Pliocene, when it filled the place formerly occupied by Fossacallista. Notocallista s. str. probably split off from Striacallista in Australia about the Upper Pliocene for the oval variety of the Kalimnan N. submultistriata has much in common.

Two other New Zealand Tertiary members of the Pitarinæ are discussed below. Hyphantosoma Dall and Rohea n. gen. Hyphantosoma is a West Indian group with zig-zag sculpture. The New Zealand species, sculpturatus Marshall may have developed this peculiar sculpture independently. Zig-zag colour patterns occur widely in the family and perhaps indicate the common base from which the grooves developed. However, until more definite evidence to the contrary is available, sculpturatus should be classed under Hyphantosoma.

Although the affinities of its hinge are with the European Cretaceous Callista, Rohea could be explained, because of the similar sculpture and ligament as an offshoot from Fossacallista. The sculpture of the whole subfamily, however, is so simple that resemblance in this respect does not carry much weight, therefore the evidence offered by the hinge has been given preference.