3. Genus Callistina Jukes-Brown.

Type: C. plana Sowerby.

Subgenus Tikia n. subgen. (from Tiki — one of the first men according to Maori myth).

Type: Callista thomsoni Woods.

Shell large, oval, strong. Lunule rather deeply impressed, clearly defined by the bounding ridge, but with no incised line; escutcheon deep, smooth. Sculpture of strong, distant, bevelled ridges with concave interspaces. Left valve with very long thin posterior cardinal joined to nymph, median cardinal of moderate strength, bevelled, not grooved, joined above to anterior cardinal which is laminar, anterior lateral tooth extremely long, the posterior half swollen, thicker and slightly higher than the anterior part; right valve with long, strong, triangular, broadly-grooved posterior cardinal, stout, triangular, unequally-divided median and short laminar anterior cardinal, anterior lateral pit long, broad, and deep, communicating by broad, ogee curve, with space betwen two front cardinals. Valve margins smooth.

This shell was classed as Callista (Callistina) by Woods (1917, p. 32), but Callista can be used in this sense only by a disregard of the rules of priority, for it was first employed binomially by Gray for Venus verrucosa L. and so is a synonym of Clausina Brown, one of the Antigona group of genera. Tikia resembles Callistina in the very long left posterior cardinal separated from the nymph by a groove in the broad area in front of the cardinals, also in the shape and disposition of the cardinals themselves. It differs, however, in the extremely long left anterior lateral with its high knobbed posterior end, and in the huge left anterior pit. The sculpture of strong concentric ridges is also distinct from Callistina, but there seems to be a connexion through C. wilckensi which has ridges on the early shell becoming obsolete later.

Callistina (Tikia) thomsoni (Woods). (Figs. 55, 56).

1917. Callista (Callistina) thomsoni Woods, N.Z. Geol. Surv. Pal. Bull. No. 4, p. 32, pl. 17, figs. 4, 5, 6, 7.

Figure 7 of Woods represents a specimen with well-preserved sculpture of distant ridges. The writer can find no grounds for separating this from C. thomsoni, traces of the same sculpture of distant strong ridges remain on the types and the difference in height of the umbos can be accounted for by the decorticated condition of the original of figure 6. The difference of outline is not so apparent in the specimens themselves as in the figures.

The hinges of Woods's syntypes have now been cleared of the hard matrix and are figured below.

Locality: 587, Selwyn Rapids (Upper Senonian).