Pectinidae.

Lentipecten parki n.sp. (Plate 23; Figs. 7, 10, 13.)

Shell fairly large, almost equilateral and equivalve except for the ears. Dorsal margins slightly concave, apical angle increasing from about 110° to about 125°. Surface smooth, but having extremely fine, regular, concentric grooves, about 12 per mm. Ears subequal, relatively very long, those of the left valve with a remarkably straight dorsal margin and almost rectangular corners, those of the right valve with a strongly but irregularly serrate dorsal margin. Right anterior ear with a moderately deep byssal notch which, however, does not form a radial groove or ridge. Both ears of the right valve set on a plane oblique to that of the disc and separated from it by a step or ramp which gets rapidly broader distally. Internally, the hingemargin is narrow, and quite intersected by the resiliary pit.

Height, 55 mm.; length, 57 mm.; inflation (1 valve), 8 mm.

Localities: Hampden Beach (type); G.S. 2572, Waihao Downs; G.S. 164, Greensands, Kakahu (Bortonian Stage); G.S. 2873, Ten Mile, Greymouth, near top of Island Sandstone (? Tahuian).

This shell is, of course, very like the widespread Miocene L. hochstetteri (Zitt.), and has been so identified (under the synonym P. huttoni Park) in most lists of Hampden mollusca. The two species are easily distinguished by their ears. In the left valve; the ears of hochstetteri (Plate 23, fig. 12) have a much shorter dorsal margin having, at its extremities, obtuse angles of about 120°. The long, straight dorsal margin of the ears of L. parki (Plate 23, fig. 13) forms with the anterior and posterior vertical margins an approximate right angle. In the ears of the right valve the dorsal margin is straighter and the distal angles are rounded and obtuse in hochstetteri (Plate 23, fig. 9), but they are sharp and subrectangular in parki (Plate 23, figs. 7, 10). Further, the bysal notch of parki is considerably deeper, but the shallow sinus of hochstetteri forms a low radial bulge.