BIVALVIA. 39 



I have seen tins from one locality only. The solitary line spoken of by Mr. 

 Sowerby, in ' Mill. Conch.,' as generally running clown the centre of the interspaces, is a 

 character not constant ; in some it is not visible, while in others this space is occupied 

 with several lines. The spaces between the ribs are not quite so wide as the ribs 

 themselves, and these show fine curving and radiating striae. The keel in some 

 individuals is large and strong, giving an almost angular form to the rib ; but in 

 general this keel is merely a sharp line upon the otherwise rounded costae, closely ap- 

 proaching P. recondittts. The auricle on the pedal side is slightly the larger of the two, 

 and in the right valve this auricle is costated and sinuated beneath, with three or four 

 denticulations upon the margin of the shell. 



3. Pecten corneus, /. Soioerby. Tab. IX, fig. 7, a — d. 



Pecten corneus. J. Sow. Min. Conch., t. 204, 1818. 



— — Id. in Dixon's Geol. of Sussex, t. 4, fig. 6, 18.50. 



— — Nyst. Coq. Foss. Belg., p. 299, pi. 23, fig. 1 a, I, 1843. 



— — Morris. Cat. Brit. Foss., p. 178, 1854. 



Spec. Char. P. testa tenuissimd, orbicidato-depressd vel jjlano-lenticulatd, (prpiilaterali, 

 laevigata, vel obsolete striata ; striis irregularibus ; umbonibus acutis j aitriculis subceaua- 

 libus, rectangidis, superne prominentibus, tenuissime striolatis. 



Shell very thin, orbicular, depressed, or of a flattened lenticular form ; smooth, or with 

 fine, nearly obsolete striae ; beaks sharp ; auricles nearly equal, rectangular ; generally 

 with fine radiating striae. 



Diameter, 2| inches. 



Localities, Bracklesham, Bramshaw, Brook, Stubbington {Edwards), Cuffell [Prest- 

 wicli); var. corneolus, Highgate {WethereU). 



Belg., Les sables de Lacken, Jette, Foret, St. Gilles [Nyst). 



This species is abundant at Bracklesham, but, on account of its extreme tenuity, is not 

 very common in cabinets. Our shell, which is smooth to the naked eye, exhibits under a 

 common hand-glass fine diverging striae, most distinct near the margins of the shell, and in 

 well-preserved specimens they are plainly visible all over ; it is also rayed irregularly on 

 the inside. The auricles are plain and smooth, except under a magnifier, when the same 

 kind of fine radiating striae may be seen as are upon the shell. There are at the 

 base of the auricles, on the interior, two prominent diverging teeth, those in the right 

 valve being higher and smaller than in the other, and the adductor muscle-mark is very 

 conspicuous, generally of a darker colour ; this is large and rounded, and in the right 

 valve, which is the deeper or more convex one, it is higher in the shell or nearer to the 

 hinge than in the left or flatter valve, where it is more in the centre, giving a more 

 powerful action to that valve, and the mark of the mantle is visibly impressed upon the 

 interior. The shell is nearly orbicular, but sometimes the diameter is greater longi- 



