BIVALVIA. 109 



2. Nucula bisulcata, /. Sowerbg. Tab. XVIII, fig. 13, a — c. 



Nucula bisulcata. J. Sow., in Dixon's Geol. of Sussex, pp. 93, 170, t. 2. fig. 13. 18.50. 

 — — Morris. Catal. Brit. Foss., p. 217, 1854. 



Spec. Char. N. testa ovato-subtrigond, elongatd, crassd, laevigata ; pedi-regione 

 ettipticd, longiore et altiore ; siphoni-regione angulatd, subproductd, compressiusculd ; lunula 

 elongato-lanceolatd, bisulcata; ano ovato, in medio prominente ; dentibus ad apicem gradafim 

 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, N. Cumingii, from the Indian Archipelago, but 

 from which it differs, according to description, in not having the lunule with a bipartite 

 division. 



3. Nucdla Bowerbankii, /. Sowerbg. Tab. XVIII, fig./, 14, a, b. 



Nucula Bowerbankii. J. Sow. Geol. Trans., 2nd series, vol. v, t. 8, fig. 11, 1834. 



— — Prestwich. Geol. Joura., 1847, p. 405. 



— — Morris. Cat. Brit. Foss., p. 217, 1854. 



Spec. Char. N. testa late ovatd, subtrigond, valde inaquilaterali, convexd, radiatim 

 striata ; striis depressis, latis, approximatis ; siphoni-regione oblique truncald ; lunula 

 elongato-lanceolatd vix perspicud ; marginibus crenulatis. 



" Elliptical, convex, smooth externally, striated within ; anterior (?) extremity obliquely 



