NUCULA. 13 
Affinities. —The characters in which this species differs from N. ovata, Mantell, 
are—(i) the greater curvature of the ventral margin, (ii) the angular form of 
the posterior end of the shell, (iii) the absence of the constriction at the ventral 
margin, (iv) the absence of the sinuosity at the postero-ventral angle, (v) the usually 
more distinctly limited lunule. The characters 1, 11, and v also serve to separate 
N. planata from N. obtusa, Sowerby. In N. impressa, Sowerby, the shell is 
smaller and relatively shorter, and the lunule more depressed and relatively wider 
than in N. planata. N. Cornueliana, d’Orbigny,’ appears to me to be very closely 
allied to, if not identical with, N. planata, and is regarded by Pictet and Campiche 
as simply a variety of N. planata ; they state that it differs from the latter in being 
proportionately thicker, and in having the anterior part of the shell shorter, so 
that the apical angle is a little smaller. In N. simplex, Deshayes, the posterior 
part is much shorter than in N. planata. 
Types.—I have not seen the type. There are examples in the d’Orbigny 
Collection in the Museum of Natural History, Paris. Specimens figured by 
Gardner are in the Woodwardian Museum, and in Mr. Meyer’s Collection. A 
specimen which is regarded as the original of Phillips’s N. ovata is preserved in 
the York Museum. 
Distribution.—Speeton Clay (C 8 and D 4); Crackers of Atherfield; Perna bed 
of Redcliff, Isle of Wight. 
Nocuta, sp. Plate II, figs. 16 a, b, 17. 
1884. Nucurna Cornvenrana, J. 8. Gardner (non d’Orbigny). Quart. Journ. 
Geol. Soc., vol. xl, p. 129, pl. v, figs. 5, 6 (non S—10). 
Description.—Shell oval, rather convex, smooth except for growth-lines. Pos- 
terior part short. Anterior extremity rounded. Postero-dorsal margin nearly 
straight, forming with the ventral margin almost a right angle. Ventral margin 
slightly curved. Lunule distinct, elongate. 
Measurements : 
Length : ; . ‘ 17 mm. 
Height F : : , 12 ,, 
Thickness (approximate) . : 2 3 
1D’ Orbigny, ‘ Pal. Frang. Terr. Crét.,’ vol. ili (1844), p. 165, pl. ece, figs. 6—10. De Loriol,‘ Anim. 
Invert. Foss. du Mte. Saléve’ (1861), p. 84, pl. x, fig. 6. Pietet and Campiche, “ Foss. du Terr, Crét. 
Ste. Croix ” (‘ Matér. Pal. Suisse,’ ser. 4), pt. iii, p. 406, pl. exxix, fig. 8. Non J. 8S. Gardner, ‘ Quart. 
Journ. Geol. Soc.,’ vol. xl (1884), p. 129, pl. v, figs. 5—10. 
