•262 



MALACOZOA. TROPIOPOOA. LAMELLIBRANCHIATA. 



teeth, four depressions, and an anterior obtuse ridge. 

 Ligament external, considerably sunk by an elevation of 

 the margins. Muscular impressions rather small, sub- 

 marginal ; paUial impression invaded by a very long, ob- 

 lique tapering sinus. 



1 Cytherea exoleta. Worn Cytherea. 



Shell orbicular, subequilateral, moderately convex^ with 

 concentric regular strise, and stronger growth-lines, somewhat 

 obsolete along the middle of the valves ; the depression cor- 

 date, sublamellate, abruptly defined; inner surface dull, but 

 with the muscular impressions, oblique mark, and margins 

 glossy ; the colour yellowish-white or reddish-wliite, with ra- 

 diating purplish or reddish bands; inside white. Diameter 

 two inches and a-half. 



The form varies little, but the colouring presents con- 

 siderable difference, it being sometimes uniform, without 

 bands, sometimes blotched or spotted. 



Very uncommon, occurring along the coast, in sand. I 

 have never met with it alive, 



Venus exoleta. Linn. Syst. Nat. i. 1134. — Venus exoleta. Penn. 

 Brit. Zool. iv. 94. PI. 54. f. 49. A; Ed. 2. iv. 209. PL 57. f. 3.— 

 Venus exoleta. Mont. Test. Brit. 116. — Cytherea exoleta. Flem. 

 Brit. Anira. 445.— Cytherea exoleta. Turt. Brit. Biv. 162. PI. 8. 

 f. 7. — Cytherea exoleta. Lamk. Syst. vi. 572 j Ed. 2. vi. 314. 



2. Cytherea Uncta. Glossed CythercBa. 



Shell orbicular, inequilateral, moderately convex, with fine 

 concentric regidar thin striae, more prominent at either end, 

 and a few stronger growth-lines ; the surface glossy ; the de- 

 pression cordate, striato-lamellate, abruptly defined ; the colour 

 greyish - white, without markings ; the inside dull -white. 

 About an inch and a-half in diameter. 



Closely allied to Cythersea exoleta, but with the dorsal slope 

 longer, the sm-face glossy, the concentric lines finer, thin- 

 edged, and more elevated at either end. 



Young shells are rather longer than high, but in older indi- 

 viduals the height considerably exceeds the length. 



On the sandy coasts, common. Sometimes brought up on 

 the fishing-lines. 



Cytherea lincta. Flem. Brit. Aniin. 445. — Cytherea lincta. liamk. 

 Syst. V. 573; Ed. 2. vi. 315. — Venus exoleta. Penn. Brit. Zool. It. 

 94. PI. 56. f. 49.— Cytherea sinuata. Turt. Brit. Biv. 163. 



