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 l'extremite anterieure." 



A recent species from the Straits of Malacca, figured and described by Mr. Hanley 

 under the name of N. marmorea (' Monog. of Nuculidse,' p. 48, pi. v, fig. 145), appears, 

 from representation, to be its nearest relative. 



12. Nucula nudata, S. Wood. Tab. XX, fig. 4, a, b. 



Spec. Char. N. testa ovato-trigond, transversa, tenui, valde incequilaterali, laevigata ; 

 margine dorsali vix incurvatd, margine ventrali convexiusculd ; pedi-regione ovato-rotundatd ; 

 1 unuld inconspicud ; ano depresso, ova to ; 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, ird of an inch. 



Locality. Headon Hill [S. Wood). Brockenhurst ? {Edwards). 



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 N. Ileadonensis, 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 N. lissa, 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 N. 

 nudata; in N. lissa, there is also a more distinct sinus 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 N. lissa that angle is very obtuse. 



13. Nucula tr^longa, Edwards, MS. Tab. XIX, fig. 4 a, b. 



Spec. Char. N. testd clongato-ovatd, pralongd, laevigata, tenui, convexiusculd, inaqui- 

 laterali ; pedi-regione ovato-rotundatd; siphoni-regione oblique truncatd ; lunula elongato- 



16 



