84 MOLLUSCA FROM THE CRAG. 
3. Nucuxa TENuIS, Montague. Tab. X, fig. 5, a—é. 
ARCA TENUIS. Mont. Test. Brit. Suppl., p. 56, t. 29, fig. 1, 1808. 
— — Pennant. Brit. Zool., vol. iv, p. 218, fide Gould. 
— — Dillw. Desc. Cat. Rec. Shells, p. 246, 1817. 
—_ — Turt. Conch. Dict., p. 11, 1819. 
— —_ W. Wood. Ind. Test., Anca, p. 47, pl. 10, fig. 45, 1825. 
Nucuna TENvIS. Turt. Brit. Biv., p. 177, 1822. 
— — Flem. Brit. Ann., p. 402, 1828. 
— — Brown. Mlust. Conch. Gr. Brit., pl. 25, fig. 13, 1827. 
_ — Gould. Iny. Massach., p. 105, fig. 64, 1840. 
— — Moller. Ind. Moll. Groén., p. 17, 1842. 
—_ _ Mace Gill. Moll, Aberd., p. 244, 1843. 
— — Morris. Cat. Brit. Foss., p. 95, 1843. 
— _ Thorpe. Brit. Mar. Conch., p. 105, 1844. 
— —_— Forbes. Geol. Surv., vol. i, p. 83, 1842. 
— — Hanley. Rec. Shells, vol. 1, p. 171, pl. 10, fig. 45. 
— — Alder. Cat. Moll. North. and Durh., p. 79, 1847. 
—_ -— Lovén. Ind. Moll. Seand., p. 34, 1846. 
— ao Forb. and Hanl. Uist. Brit. Moll., vol. ii, p. 223, pl. 47, fig. 6 (Animal), 
pl. P, fig. 5, 184 9. 
—  eNERA. S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 295, pl. 14, fig. 2. 
— Rycxuortrana? WNyst. Coq. Foss. de Belg., p. 233, pl. 15, fig. 10, a—é, 1844. 
—  ovecriprens. Phil. En. Moll. Sic., vol. ii, p. 48, t. xv, fig. 15, 1844. 
— tvcia. Blanding. MSS. fide Gould. 
Spec. Char. Testd ovatd, trigono-ellipticd, levigatd, tenui, latere antico subangulato ; 
lunulaé parum distinctd, margine ventrali arcuato, integro. 
Shell ovate, elliptically triangular, smooth, and thin; anterior side produced, 
roundedly angular; junule not well defined, ventral margin smooth. 
Diameter, } an inch. 
Locality. Cor. Crag? Gedgrave. 
Red Crag, Bawdsey. 
Mam. Crag, Bridlington, Chillesford. 
Recent, Mediterranean, Britain, Scandinavia, and North America. 
Two specimens of a species resembling this are in my Cabinet, they were obtained 
from the Coralline Crag, but are too imperfect for correct determination. In the 
Red Crag Formation it has undoubtedly made its appearance, several individuals were 
found by myself, and in the sandy deposit at Chillesford it is an abundant shell 
seemingly increasing in numbers towards the present Period. Its greater tenuity and 
more ovate form will distinguish this from JV. nucleus, as well as the absence from the 
margin of all crenulations. It differs from the young of JV. /evigata in being less 
transverse, that species having a greater diameter when measured from the anterior 
to the posterior margin, the hinge line also forms a greater angle than in ¢eawis, and 
the posterior termination is somewhat produced. In this species the anterior dorsal 
margin is more rounded than in any of the others, so is the ventral margin, 
