138 J. S. GARDNER ON BRITISH CRETACEOUS NUCULID. 
specific name is necessary, unless the Speeton and the Gault forms 
are to be united. There is a similar shell in the British Museum 
from Atherfield. 
Gault Species. 
Lepa Marra, d’Orb.,sp.,Pal. Frane., Terr. Crét. vol. iii. p. 169, pl. 301, 
fig. 4-6 (1843). Plate IIT. figs. 28-29. 
The dimensions of this shell are usually much under those I have 
tabulated. It is skiff-shaped, with the anterior hinge-margin con- 
cave and terminating anteriorly in a more or less produced or 
rounded and obtuse rostrum, while the posterior margin is blunt and 
irregularly rounded and the inferior margin strongly and slightly 
sinuously curved. It is a smaller and much more compressed 
shell than those hitherto described, and, unlike them, the valves are 
more frequently detached than otherwise. It is striated, except 
towards the extremities, which are smooth, as in ZL. subrecurva. 
D’Orbigny’s description points to a larger and less compressed shell 
with a less central umbo; but his specimens show the species to be 
the same. Pictet mentions a length of 14 millims. 
The species is very common in the Lower Gault of Folkestone, and 
appears to pass unchanged into the Folkestone Beds of the Lower 
Greensand and into the Upper Gault. The variability of the shell 
precludes me from fixing any specific character by which to distin- 
guish it from ZL. angulata, Sby., from Blackdown; but it is a more 
elongate and delicate shell, and I hardly like to reunite them on the 
present material. 
Blackdown Species. 
Leps anevunata, Sby., sp., Min. Conch. p. 120, pl. 476, fig. 5 (1828). 
Plate IV. figs. 17-19 
There are no definable characters by which this can be distinguished 
from L. Maric, but the latter appears to be more delicate and more 
elongated or rostrated. It is, however, so variable a shell in the 
Gault that some specimens come well within the form of the Black- 
down types, though the latter seem less compressed and have a slightly 
denticulated margin. To determine whether sufficient modification 
had taken place during the lapse of time between the deposition of 
the Gault and the Blackdown beds to have furnished new specific 
characters, would require a very large series from the latter and an 
acquaintance with the marginal and hinge-characters of the former. 
In the mean time it appears useless to exchange D’Orbigny’s well- 
known name in favour of the nearly obsolete name of Sowerby, and 
by retaining the two names we at least mark the difference in 
horizon and perhaps of species. 
Neocomian Species. 
Lepa scapHa, d@Orb., sp., Pal. Frang., Terr. Crét. vol. ii. p. 167, 
pl. 301, figs. 1-3. Plate V. figs. 21-23. 
This shell resembles the Gault species, Z. Marie, in the closest 
