much confused. The shells are of oval shape and have an anterior lateral tooth or tubercle in the left valve with a corresponding pit in the right; the sculpture consists of regular concentric lamellae or ridges, sometimes reticulated by radial ribs, and the valve margins are crenulated. Dall considered that the anterior lateral tubercle was a true decadent lateral tooth of the same origin as the lateral tooth of Macrocallista, and said that it was an “excellent index to important anatomical differences.” He therefore classed the group under the genus Cytherea Bolten (type V. puerpera L.) recognizing many subgenera and sections, and put it in the subfamily Meretricinae. Iredale (1914, p. 668) showed that Cytherea Bolten was preoccupied and that Antigona Schumacher (type Antigona lamellaris Schum.) was the oldest name for the group.

Later, Jukes-Browne (1914, pp. 71 and 76) pointed out that the anatomical differences supposed by Dall to be correlated with the lateral tooth had not been demonstrated; so taking into account the other shell characters he thought that Antigona was more closely related to the Venerinae. Yet he was content to leave the genus in the Meretricinae so as to facilitate the division into two subfamilies according to the presence or absence of an anterior lateral tooth. In doing so he made the extraordinary statement “our genera are established for the sake of convenience in classification and not for the purpose of expressing a theory.” Surely our classifications are the expression of theories of relationship. If they are not they can hardly claim to be “Natural” Science.

Cossmann, following Roemer and Fischer, did not grant the anterior tubercle generic significance, the shells concerned being classed as subgenera of Chione, which thus included even such as Ventricoloidea Sacco, type V. multilamella Lamarck.

It may be mentioned here that in his revision of the Veneridae Jukes-Browne overlooked Ameghinomya Ihering, 1907 (type Ch. argentina Iher.) which closely resembles Periglypta.

The Tertiary rocks of New Zealand are fairly rich in shells which are related to Antigona, and the species, Kuia vellicata (Hutton), has an extremely strong lateral tooth, stronger indeed than some of the cardinals. An examination of the young stages of these shells shows that the anterior lateral in the Antigona group has an origin quite different from that of the Meretricinae. In Macrocallista the left anterior lateral is the continuation of a low ridge proceeding from below the umbo, diverging from and in no way connected with the anterior cardinal. This is shown very clearly in Grateloupia and Macrocallista. In Antigona and its allies, however, the left anterior cardinal is triangular and it is the anterior prolongation of this tooth along the hinge-margin which has given rise to the lateral tooth. This is clearly revealed in the ontogeny of species of Kuia figured below.

This difference in origin of the lateral tooth of Antigona from that of Macrocallista harmonises with the other shell characters, such as ornamentation, crenulation of the margins, and arrangement of the cardinal teeth which in Antigona resemble those of the Venerinae.

The use of a single genus to cover the whole of this group emphasises a unity of relationship that may not accord with the facts, for the development of the anterior lateral tubercle could take place in parallel groups. Further, so many diverse and easily-distinguished forms are included that the classification of all under Antigona is

Fig. 2.—Kuia vellicata (Hutton) Target Gully, showing stages in the development of the anterior lateral tooth. a, 1.5 mm. long; b, 2.25 mm.; c. 3 mm.; d, 5 mm.

clumsy. It seems better to grant generic rank to most of the subgenera and sections recognised by Dall. Jukes-Browne synonymized Ventricoloidea Sacco with Artena Conrad, but the two are easily separated. The anterior lateral tooth of Ventricoloidea multilamella Lamk. is strongly developed, in Artena staminea Conrad it is the merest tubercle. Other differences are shape, sculpture, and arrangement and relative strength of the cardinal teeth.

The new genus Kuia described above possesses much in common with Ventricoloidea indeed Cossmann (in Marshall 1917, p. 462) has already classed the type, K. vellicata in that genus. There are, however, important differences which indicate that relationship is not so close as the external resemblances might lead one to suppose. The median cardinals of Kuia are both very narrow and bifid, but those of Ventricoloidea are thick, especially that of the left valve which, further, is not divided. The right posterior cardinal of Kuia is much shorter and stouter than that of Ventricoloidea and the divergence of the two right anterior cardinals is very much greater so as to accommodate the very strong left anterior cardinal.

Kuia vellicata (Hutton). (Figs. 92–95.)

1873 Chione vellicata Hutton, Cat. Tert. Moll., p. 21.

1886 Venus meridionalis Sowb. Hutton, Trans. N.Z. Inst., vol. 18, p. 362, (not of Sowb.).

1914 Chione meridionalis (Sowb.), Suter, N.Z. Geol. Surv. Pal. Bull., No. 2, p. 51, pl. 14, fig. 4.

1917 Chione (Ventricoloidea) vellicata (Hutton), Cossmann in Marshall, Trans. N.Z. Inst., vol. 49, p. 462.

1917 Cytherea (Circomphalus) chariessa Suter, N.Z. Geol. Surv. Pal. Bull., No. 5, p. 74, pl. 10, figs. 3, 4.

It will be seen that while Hutton and Suter considered this shell to be the South American C. meridionalis, Cossmann was quite opposed to them. The lectotype of K. vellicata from Awamoa, is a decorticated left valve, embedded in an extremely hard matrix which conceals most of the hinge and indeed the whole interior. An anterior lateral tooth has, however, been disclosed on excavation. Topotypes also show that this shell is certainly not a Chione (except in the sense of Fischer and Cossmann) for there is a strong anterior lateral in the left valve and a deep pit, with a lateral above and one below, in the right valve. The specimens handled by Cossmann were from Target Gully and so in a fine state of preservation. He said that they had no analogy with C. meridionalis and placed them under Ventricoloidea.

C. meridionalis belongs to Ameghinomya v. Ihering, and so is but distantly related to K. vellicata.

The right posterior cardinal of K. vellicata is deeply grooved along its entire length; the median laminar but bifid; the anterior entire and widely diverging from the median. The left anterior cardinal is thick and strong, triangular in cross section, with a high point, and often vaguely grooved on the ventral surface; the left median cardinal is very narrow, and deeply bifid. Both Hutton and Suter mention radial sculpture on this shell and, indeed, this was the main reason for synonymizing with C. meridionalis. The radials, shown so clearly by the holotype of K. vellicata are merely the internal structure revealed by weathering, a feature liable to be developed on all shells with a crenulated margin. There is no trace of radial sculpture on well-preserved specimens except on the lower surface of the laminae.

Specimens from Target Gully were identified by Suter at different times as Chione meridionalis, Cytherea sulcata, and Cytherea subsulcata; obviously his conception of these species was extremely confused.

Hutton's syntypes from the various localities mentioned by him in 1873 are no longer available, but it is practically certain that more than one species was represented.

The writer was at first inclined to let K. chariessa stand as a separate species because of its fine sculpture, but an extensive series