26 CRETACEOUS LAMELLIBRANCHIA. 
growth, crossed by very indistinct radial ribs. Margin crenulate. Hinge and 
adductor impressions not seen. 
Measurements : 
(1) (2) (3) 
Length . : 7 MO : 9 : 8 mm. 
Height . ; : 8 : 7 ‘ i 
Affinities. —This species is distinguished from N. impressa, Sowerby, by its 
more triangular outline and larger lunule. It is less convex and proportionately 
longer than N. antiquata, Sowerby, and has less prominent umbones. It is 
smaller, more pointed at the extremities, and has a deeper and more sharply 
limited lunule than N. albensis, d’Orbigny. 
Types.—In the British Museum. 
Distribution.—Lower Gault (zones y, vi, and vi) of Folkestone. 
Nucua anriquata, Sowerby, 1824. Plate IV, figs. 22 a—c, 23a, b, 24a, b, 25, 26. 
1824. Nucuna antiquatra, J. de C. Sowerby. Min. Conch., vol. v, p. 118, 
pl. cecelxxy, fig. 4. 
1854. -- — J. Morris. Cat. Brit. Foss., ed. 2, p. 217. 
1866. — — F. J. Pictet and G. Campiche. Foss. du Terr. Crét. de 
Ste. Croix (Matér. Pal. Suisse, ser. 4), pt. 3, p. 418. 
i884. — — J. S. Gardner, Quart. Journ. Geol. Soe., vol. xl, 
p. 184, pl. iv, figs. 3—S. 
Description.—Shell very convex, triangular, posterior angle rounded, anterior 
somewhat pointed ; ventral margin curved. Umbones prominent, curved, placed 
very posteriorly. Lunule very broad, cordate, smooth, depressed, sharply 
defined. An anterior area is cut off by a ridge passing from the umbones to the 
anterior margin. Surface ornamented with fine, slight, radiating ribs crossed by 
well-marked concentric growth-lines. Margins crenulate. Anterior part of the 
hinge-line has about twenty teeth, and is bent almost at right angles to the 
posterior part, which has about nine teeth; the anterior part is more than twice 
the length of the posterior part. Adductor impressions rounded, the anterior 
being the larger. 
Measurements : 
(1) (2) (3) (4) 
Length . . ; ee ge Us IK) eb aang 
Antero-dorsal margin 5 lee SO, OR Las 
Postero-dorsal margn . 6 . 45. 45 . O ,, 
Height. : ; a Ss Sh BO Se CY 
Thickness ; F SD ES —- .-— , 
