BIVALVIA. 91 
so much so as in Z. /anceolata, and the muscular marks are then deeply impressed, 
those produced by the adductors are of a subovate form, and are unequal in size, the 
anterior one being the larger, and the sinus formed by the mantle extends about as far 
inwardly as the posterior part of the ligamental pit, which is broad and contracted in 
the centre. 
Our shell appears to correspond with the recent American species to which 
it is here assigned, in all its characters, excepting size. Dr. Gould gives the dimen- 
sions of his shell as 1,1; inch in its largest diameter, which is considerably less than 
the magnitude to which our fossil has attained. In the recent state it is generally 
eroded at the beaks; our fossil does not appear to have been at all acted upon at 
that part, it is there quite perfect. 
A shell from the Antarctic Seas, WV. Hightsii, Couthouy, strongly resembles our 
British fossil. 
3. Lepa sEmristriaTa, S. Wood. Tab. X, fig. 10, a—é. 
Nucura semistriata. S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 297, pl. 14, 
fig. 5, 1840. 
— niripa. Nyst. Rech. Coq. Foss. d’Anv., p. 16, pl. 3, fig. 62, 1835, (not Brocchi.) 
— oepressa. Nyst. Coq. Foss. de Belg., p. 220, pl. 15, fig. 7, 1844. 
Spec. Char. Testa transversd, ovato-ellipticd, subaquilaterd, compressa, tenuissimi, 
fragili ; antice rotundato-ovatd et levigatd, posticé subrostratd et transversim striata ; 
natibus approximatis, margine integerrimo. 
Shell transverse, elliptically ovate, subequilateral, compressed, thin, and fragile ; 
anterior side roundly ovate and smooth; posterior subrostrated and transversely 
striated ; beaks approximate, margin quite smooth. 
Longest diameter, \ inch. 
Locality. Cor. Crag, Sutton and Ramsholt. 
This shell is abundant in the Coralline Crag at Sutton, but from its great fragility 
specimens of the above dimensions are very rarely obtained, and if it be the same as 
the Belgian fossil, which I presume is the case, M. Nyst speaks of it as being by no 
means rare in the Campinian Beds. 
The strize or transverse ridges upon our shell are rounded and obtuse, not sharp 
or imbricated; they cover the posterior half of the exterior, extending from a little 
beyond the centre or umbo to the extremity, but often become irregular and obsolete 
upon the posterior slope, and the shell is there depressed and subsinuated with a very 
slightly recurved and somewhat pointed termination at the extremity of the dorsal 
edge. From the extreme thinness of the shell the transverse edges are often visible 
in the interior; a long line of sharp angularly formed and prominent teeth occupy 
the hinge area, amounting in large specimens to as many as five and twenty on the 
anterior, with twenty or more on the opposite side, while in young ones they are not 
above half that number: they are separated by a rather large and obtusely angular 
