34 LIN'.VEAN GENEP.A. 



Genus 9.— DON AX. 



Animal a Tetbys ; shell bivalve, with generally a crenulate 

 margin, the frontal margin very obtuse ; hinge with two teeth, 

 and a single marginal one 'placed a little behind, rarely double, 

 triple or none. 



Donax truncidus. — The Truncated Don ax. Plate IV. 

 fig. 6. and plate VI. fig. 9. Transverse, oblong, glossy, finely 

 striated longitudinally, and transversely banded and radiated with 

 purple ; white, clouded with purple within ; internal margin 

 crenulated. Inhabits the British coasts. 



The shells of this geous are transverse, triang-iilar, inequilateral, flattened, 

 truncated before, and wedge-shaped. They inhabit the ocean ; lurking iu 

 the sand of the shore, and may be found on the reflux of the tide. 



Genus 10.— VENUS. 



Animal a Tethys ; shell bivalve, the frontal margin flattened, 

 with incumbent lips ; hinge with three teeth, all of them ap- 

 proximate, the lateral ones divergent at the tip. 



This genus is divided into two sections : pubentes * and impubentes.** 

 This latter section is sub-divided into three families : siib-cordate,f orbicu- 

 lar,tt aud oval.ff f 



Venus Chione. — Tfie Chione Venus. Plate I. fig. 4. 

 (Cytherea Chione, Lamarck.) Shell strong, sub-cordated, 

 somewhat concentrically wrinkled, margin entire, covered with 

 a smooth, glossy, chestnut-coloured epidermis ; sometimes a 

 little radiated ; beneath which the shell is of a beautiful pale 

 purple; apt'X turned sideways, with a cordiform depression ; 

 umbo placed nearest one end. Inhabits the sea at Falmouth in 

 Cornwall. 



a a Summit, b b lunule, i anterior slope, k posterior slope, o disk, p margin 

 or limb. 



Venus compiessa. — The Compressed Venus. Plate I. 

 fig. 6. (Crassina compressa, Leach.) Shell strong, thick, sub- 

 orbicular, compressed, and slightly sulcated or irregularly wrin- 

 kled ; colour white, but is usually covered by a thick yellowish- 

 brown epidermis ; umbo prominent, turning to one side, beneath 

 which is a small cordiform depression ; hinge with two teeth in 

 one valve, and a transverse one. Inhabits the British seas. 

 c Sides, d base, e e cicatrix, g g teeth of the hinge, iv the umbo. 



Venus decussata. — The Decussated Venus. Plate I. fig. 



