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Genus Venericardia Lamarck, 1801.
Type: Venericardia imbricata Lamk.
Venericardia christiei n. sp. (Figs. 23, 28, 30.)
Shell large, heavy; beaks prominent, near anterior end. Lunule deeply sunk, convex in youth, but sloping inwards as growth proceeds, bounded by an incised line. Escutcheon shallow, not well defined. Sculpture of about 24 strong, rounded radial ribs, with well-marked interstices of about same width. Close, regular growth-striae cover the shell but are stronger in interstices, also ribs have indications of obscure nodes at intervals. In spite of these irregularities the surface has a smooth shining appearance. Hinge deep and strong, teeth well grooved; left valve with the inward sloping lunule only slightly invading anterior cardinal tooth with which it forms an angle of 30°. Right valve with a broad median cardinal well separated from thin anterior cardinal which in turn is distant from lunular margin; posterior cardinal forming rudimentary ridge on nymph.
Holotype in Dominion Museum.
Height, 50 mm.; length, 50 mm.; inflation (1 valve), 19 mm.
This species is related to V. awamoaensis Harris (= V. pseutes Suter) but it can readily be recognized by the higher, narrower ribs and wider interspaces. The hinge-teeth, and lunule of V. christiei are not so oblique as those of V. awamoaensis, so that the space between the lunular border and the anterior cardinal is much wider. Also V. awamoaensis is usually less oblique in shape, the umbos being lower and not so far forward.
Venericardia pseutella n. sp. (Figs. 29, 31.)
Shell of moderate size, beaks prominent, about anterior fifth. Lunule small, concave, sloping forward below, scarcely invading anterior cardinal tooth above. Escutcheon not developed. Sculpture of 28 very low, smooth, rounded radials with linear interstices, ribs of posterior area narrower than others. Left hinge with two strong cardinals, anterior one forming with lunule a triangular space; posterior one arched.
Holotype in Dominion Museum.
Height, 21.5 mm.; length, 22.5 mm.
Only two incomplete left valves were collected. They closely resemble V. awamoaensis Harris but differ in having the lunule sloping forward instead of backward, almost parallel to anterior cardinal, in this respect being like V. christiei. They are readily distinguished from this shell however by the much weaker and more numerous radials.
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Venericardia caelebs n. sp. (Figs. 22, 24.)
Shell of moderate size, umbo fairly prominent, at anterior fourth. Lunule convex, cordate, sloping forward. Escutcheon not developed. Sculpture of 29 high, rounded, radial ribs with interspaces about same width; anterior two ribs and posterior one extremely weak. Ribs on anterior part of disc with regular transverse ridges, but those on posterior part almost smooth, except the fourth from last which has prominent spaced spines. Ribs on posterior area considerably weaker than those of central part of disc. Hinge of moderate width; left valve with anterior cardinal strong, triangular, well separated from arched lunular border; posterior cardinal long, arched, of moderate strength, parallel to ligamental nymph. Right median cardinal evidently very broad.
Holotype in collection of N.Z. Geological Survey.
Height, 27 mm.; length, 30 mm.; inflation (1 valve), 10 mm.
Differs from the Recent species, V. difficilis (Desh.), in having rather more ribs, which, moreover, are almost smooth over a great part of the shell. The hinge is of the same general type as that of V. purpurata (Desh.) but the left posterior cardinal is longer and further away from the anterior one, so that the right median cardinal must be considerably broader. Also the adductor-scars of the Recent shells, especially the anterior one, are much larger than in the fossil. A single left valve has been collected.