126 J. S. GARDNER ON BRITISH CRETACEOUS NUCULID. 
It appears to occur throughout the Gault, in the Cambridge phos- 
phate-beds, and at Upware (fide Keeping); but it should be removed 
trom the Speeton-Clay and Blackdown lists of fossils. Its range in 
France is comparatively restricted, and at St. Florentin it passes into 
the allied species WV. capseformis, Mich. Very perfect specimens 
with tightly closed valyes may be picked up by the score at Folke- 
stone, when the tide is out. Mr. Jesson’s collection includes 70 
specimens from Cambridge, so that it appears to be abundant there 
also. Examples of these are figured, Plate IV. figs. 28-30. 
Pictet, like D’Orbigny, confounds this species with NV. capse- 
formis, and apparently describes casts of true NV. ovata as N. 
gurgitis. 
Blackdown Species. 
Nvcuta optusa, Sby., in Fitton, Geol. Trans. 2nd ser. vol. iv. 
pl. xvii. fig. 11, p. 342 (1836). Plate IV. figs. 1-2. 
This shell is of about the same size as JV. ovata. and similarly 
smooth, marked with lines of growth and deep furrows towards the 
inferior margin, but differs very strikingly in its truly ovate form and 
regularly curved inferior margin, and in the absence of any tendency 
to constriction. The umbo also is much more forward, and the 
lunule is less defined. Itis evidently a rare shell, for it is absent from 
the private collections that I have seen, and of the three specimens 
at Bristol, one is a mere fragment, and none has the hinge perfect. 
One shows the pearly nacre under the outer layer, which is of the 
crystalline structure usual in Blackdown fossils. I have a single 
cast from the Grey Chalk of Folkestone which seems to be identical 
in every respect with .V. obtusa, presenting precisely the same 
differences from JV. ovata. It shows the muscular impression, and 
appears to have been only an interior mould when imbedded. 
The JV. obtusa described by D’Orbigny, Terr. Crét. vol. 11. p. 163, 
and figured pl. 300, figs. 1-5, as WV. planata, Desh., is certainly 
not the same species; but D’Orbigny himself subsequently rectified 
his error in the ‘ Prodrome.’ 
The specimens originally figured by Sowerby are still preserved 
in the Bristol] Museum, and I am indebted to the courtesy of the 
Keeper for the opportunity of comparing them at leisure in 
London. 
The figured specimen is from the Jermyn-Street Museum, and 
others are preserved at Cambridge and in the British Museum. 
There are specimens from the Upper Greensand of Devizes, in both 
the British and Jermyn-Street Museums, which seem to connect 
this with the true J. ovata. 
Neocomian Species. 
Nwcvta pLanara, Desh., in Leym., Mém. de la Soe. Géol. t. v. p. 7, 
pl. 9, f. 3 (1842). Plate V. figs. 1-4. 
The only difference that I observe between this and J. ovata is a 
more compressed shape, and perhaps slighter tendency to con- 
