BIVALVIA. 109 
2. Nucuna BisuLcata, J. Sowerby. Tab. XVIII, fig. 13, a—e. 
Nucuna sisutcata. J. Sow., in Dixon’s Geol. of Sussex, pp. 93, 170, t. 2. fig. 13. 1850. 
— — Morris. Catal. Brit. Foss., p. 217, 1854. 
Spec. Char. N. testdé ovato-subtrigond, elongatd, crassd, levigatd ; pedi-regione 
ellipticd, longiore et altiore ; siphoni-regione angulatd, subproductd, compressiusculd ; lunuld 
elongato-lanceolata, bisulcatda ; ano ovato, in medio prominente ; dentibus ad apicem gradatin 
minutissimis ; marginibus integris. 
Shell ovately sub-trigonular, elongated, thick, compressed, smooth; pedal region 
elliptical, margin ovately rounded; siphoni-lateral margin angulated, compressed, and 
slightly produced ; lunule elongately lanceolate, with a central ridge; anal region ovate, 
prominent in the centre; teeth diminishing towards the umbo, ventral margin smooth. 
Length, 1} inch ; height, 1 inch. 
Localities. Barton, Bracklesham. 
Specimens of this species are not very abundant, and have, I believe, been as yet only 
found at the above localities. ‘ 
The shell is nearly smooth, with the exception of distinct lines of growth. The dorsal 
margin has a sort of flattened space (lunule), with a central elevation or ridge, on each 
side of which is a depression or furrow, giving a sinuation to the pedi-lateral margin, and 
to this peculiarity of character the species.owes its name. The muscle-marks are both 
deeply impressed, the anal one more especially so; it is of an elongated form, pointed 
towards the umbo, and there is also an impression in the umbonal region, probably left by 
the retractors of the foot. The teeth are not numerous, about a dozen on the pedal side, 
and half that number on the other. The shell in the living state was probably covered 
with a thick epidermis; traces of this may be seen on many specimens. The nearest 
approach to this is a recent species, VV. Cumingit, from the Indian Archipelago, but 
from which it differs, according to description, in not having the lunule with a bipartite 
division. 
3. Nucota Bowersankil, J. Sowerby. Tab. XVIII, fig. 7 14, a, 6. 
Nucuua Bowrrpankil. J. Sow. Geol. Trans., 2nd series, vol. v, t. 8, fig. 11, 1834. 
— — Prestwich. Geol. Journ., 1847, p. 405. 
_— — Morris. Cat. Brit, Foss., p. 217, 1854. 
Spec. Char. NV. testa late ovatd, subtrigond, valdé inequilaterali, convexd, radiatin 
striata ; striis depressis, latis, approximatis; siphoni-regione oblique truncatd; lunuld 
elongato-lanceolata vir perspicud ; marginibus crenulatis. 
“ Elliptical, convex, smooth externally, striated within ; anterior (?) extremity obliquely 
