22 CRETACEOUS LAMELLIBRANCHIA. 
Measurements : 
(1) (2) (8) (4) (5) (6) (7) (8) 
Length : : - dd 29 27 26 22° 21 19 18 mm. 
Height : ; > 2k 20 17 a> 1S 7 1d) heb Ae 
Thickness . 5 ». 4 12 — — — I 9 95 
29 
Affinities.—The larger forms of this species, described by Michelin as 
N. capsxformis, and subsequently named N. Derancei by Price, have been regarded 
by some authors as distinct from Mantell’s N. ovata, but practically the only 
difference is in size: in France a perfect gradation has been traced between 
these two types; and a similar passage, although it is stated by Gardner not 
to exist, can be seen in English specimens. In England the larger forms are 
recorded by Price from zones i and ii only of the Lower Gault. N. ovata 
is related to N. obtusa, Sowerby; the points which distinguish the two are 
given on p. 23, 
Remarks.—Vhe variations in the relative proportions of the length, height, 
and thickness are fairly great, as will be seen from the table of measurements. 
The antero-dorsal border may be parallel to the ventral, or may slope more or 
less obliquely to it. The posterior extremity is commonly somewhat angular, 
but may be rounded. 
Types.—I have not been able to trace Mantell’s specimens. ‘The examples 
figured by Gardner and referred to above (except, perhaps, figs. 28 to 30) are in 
the British Museum. 
Distribution.—Through all the zones (except vii) of the Gault at Folkestone ; 
Gault of Black Ven; Cambridge Greensand (derived) ; Upper Greensand of 
Devizes. 
Nvucuta oprusa, Sowerby, 1836. Plate IV, figs. 2a, b, 3, 4a—d. 
1836. Nucuna oprusa, J. de C. Sowerby. Trans. Geol. Soc., ser. 2, vol. iv, 
p. 342, pl. xvu, fig. 11. 
1850. — — A. d’Orbigny. Prodr. de Pal., vol. ii, p. 163. 
1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 217. 
? 1866. — — F. J. Pietet and G. Campiche. Foss. du Terr. Crét. de 
Ste. Croix (Matér. Pal. Suisse, ser. 4), pt. 3, pp. 415, 
418, pl. exxix, fig. 15. 
1884. — — J.8. Gardner. Quart. Journ. Geol. Soc., vol. xl, p. 126, 
pl. iv, figs. 1, 2. 
Non 1844. — _ A. d’Orbigny. Pal. Frang. Terr. Crét., vol. iii, p. 163, 
pl. ece, figs. 1—5 (named MW. planata 
on pl. cece). 
