semisulcata Lamk. from the Moluccas and northern Australia, having a similar oval, inflated shape, well defined posterior area, and spoon-shaped chondrophore. It differs, however, in the absence of hinge plate with cardinal teeth and absence of the posterior lateral flange. It seems probable that the resemblance is only superficial. but no other group can be suggested as a closer relative.

The relations of Cardilia itself appear to be little understood, the systematic position wavering between the Mactridae and the Myidae.

Cardilona bensoni n.gen., n.sp. Plate 25; figs. 4, 5, 6.

Sculpture of about 36 rounded radial ribs, crossed by somewhat irregular growth-lines. The ribs differ considerably in strength, the 1st and 2nd from the lunule being very broad, the 6th and 7th, 13th and 14th, and 22nd to 26th narrow; the 27th and 28th are wide, the latter being rather sunk and bounding posterior wing; the 29th to 36th, on wing, are somewhat flattened and bevelled and become weaker and indefinite dorsally.

The position of the ligament is uncertain.

Height, 38 mm.; length, 30 mm.; inflation (right valve), 20 mm.

Localities: G. S. 2141, green calcareous tuffs, Bridge Point 3 miles south of Kakanui (Kaiatan Stage, Oligocene) holotype; G.S. 626, Isis bed, Campbell's Beach, Allday Bay (? Waitakian Stage, Oligocene), internal cast.

The internal cast is almost smooth, showing neither reflected sculpture nor chondrophore. The shape, the huge lunule and the strongly incurved beaks, however, leave no doubt as to generic identity with bensoni. A low rounded radial ridge on the cast occupies the position of about the 21st rib of bensoni and another radial ridge or step bounds the slightly sunken posterior wing. The muscle scars are not clearly marked, but the anterior one appears to have been fairly long and oval.

The specific name is in honour of Dr. W. N. Benson, who visited Bridge Point with Mr. D. A. Brown and the writer in 1941.