BIVALVIA. 115 
species. ‘The only difference I can perceive between the English and the French fossils is 
in the contour of the specimens ; ours being apparently a little longer and rather more 
rounded on: the pedilateral margin. Our shell is ridged concentrically, and these ridges 
are rather broad, and occasionally inosculate or undulate, like those spoken of by M. 
Deshayes, “ quelquefois un peu onduleux vers Vextremité anterieure.” 
A recent species from the Straits of Malacca, figured and described by Mr. Hanley 
under the name of V. marmorea (‘ Monog. of Nuculide,’ p. 48, pl. v, fig. 145), appears, 
from representation, to be its nearest relative. 
12. Nucuna nuvata, S. Wood. Tab. XX, fig. 4, a, 4. 
Spec. Char. N. testd ovato-trigond, transversd, tenui, valdé inequilaterali, levigatd ; 
margine dorsalt vie tncurvald, margine ventrali convexiusculd ; pedi-regione ovato-rotundatda ; 
lunula inconspicud ; ano depresso, ovato ; marginibus integris. 
Shell ovately trigonal, transverse, thin, smooth, very inequilateral ; dorsal margin nearly 
straight, ventral margin slightly curved ; pedal side roundedly ovate ; lunule inconspicuous ; 
anal region depressed ; margins smooth. 
Length, trd of an inch. 
Locality. Headon Hill (8S. Wood). Brockenhurst? (Zdwards). 
A few specimens of this species were found by myself many years ago, and I have 
considered them as entitled to the rank of a distinct species, in consequence of the ventral 
margins being quite free from denticulations, and of the outward form differing from that 
of any other smooth-margined species. 
The shell in its contour much resembles V. //eadonensis, but it is a little longer, 
more rounded, and less tumid than in that species, and it is distinguished by the 
difference of margin. It bears, also, some resemblance to JV. /issa, but it differs in two or 
three characters; in the latter species the anal or siphonal side is more pointed or 
acutely angular, the dental area shorter, and the ventral margin more rounded than in JV. 
nudata; in N. lissa, there is also a more distinct smus or lunule below the dorsal 
edge on the pedal side, and the shell is comparatively longer and thinner. The angle 
formed by the two dental lines in this species is very little more than a right angle, but 
in JV. lissa that angle is very obtuse. 
13. Nucuna pre.onca, EKdwards, MS. Tab. XIX, fig. 4 a, 6. 
Spec. Char. NV. testd elongato-ovatd, prelongd, levigatd, tenui, conveviusculd, inaqur- 
laterali ; pedi-regione ovato-rotundatd ; siphoni-regione oblique truncatd ; lunuld clongato- 
16 
