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 i, ii, 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. Gornueliana, d'Orbigny, 1 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 ; Pema bed 

 of Redcliff, Isle of Wight. 



Nucula, sp. Plate II, figs. 16 a, b, 17. 



1884. Nucula Cobnueliana, J. 8. Gardner (non d'Orligny). Quart. Journ. 

 Geol. Soc, vol. xl, p. 129, pi. v, figs. 5, 6 (non 8—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 . . . . 12 „ 



Thickness (approximate) . . . 12 ,, 



1 D'Orbigny, ' Pal. Fran?. Terr. Cret.,' vol. iii (1844), p. 165, pi. ccc, figs. 6—10. De Loriol, ' Anim. 

 Invert. Foss. du Mte. Saleve ' (1861), p. 84, pi. x, fig. 6. Pictet and Campiche, " Foss. du Terr. Cret. 

 Ste. Croix " (' Mater. Pal. Suisse,' ser. 4), pt. iii, p. 406, pi. cxxix, fig. 8. Non J. S. Gardner, ' Quart. 

 Journ. Geol. Soc.,' vol. xl (1884), p. 129, pi. v, figs. 5—10. 



