26 CRETACEOUS LAMELLIBRANCHIA. 



growth, crossed by very indistinct radial ribs. Margin crenulate. Hinge and 

 adductor impressions not seen. 



Measurements : 



(i) (2) (3) 



Length ... 10 . 9 . 8 mm. 



Height ...8.7.6,, 

 Affinities. — This species is distinguished from N. impressa, Sowerby, by its 

 more triangular outline and larger lunule. It is less convex and proportionately 

 longer thau. 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 v, vi, and vii) of Folkestone. 



Nucula antiquata, Sowerby, 1824. Plate IV, figs. 22 a—c, 23 a, b, 24a, b, 25, 26. 



1824. Nucula antiquata, J. de C. Sowetby. Min. Conch., vol. v, p. 118, 



pi. cccclxxv, fig. 4. 

 1854. — —J. Morris. Cat. Brit. Foss., ed. 2, p. 217. 



1866. — —F.J. Pictet and G. Campiche. Foss. du Terr. Cret. de 



Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, p. 418. 

 1884. — — J. S. Gardner. Quart. Journ. G-eol. Soc, vol. xl, 



p. 134, pi. iv, figs. 3—8. 



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 : 













(i) 



(2) 



(3) 



(4) 



Length 



. 13 . 



11 . 



10 



12 mm 



Antero-dorsal margin 



. 12-5 . 



10 . 



95 



11 „ 



Postero-dorsal margin 



6 



4-5 . 



4-5 



5 „ 



Height . 



. 115 . 



8-5 . 



8 



9 „ 



Thickness 



. 9 . 



7*5 . 



— 



55 



