3G6 MACTRlDiE. 



M. HELVACEA, Cliemiiitz. 



Shape inclined to oval, inequilateral ; dorsal area chestnut to 

 the very lips ; beaks coloured : lateral teeth smooth. 



Plate XXIII. fig. 2. 



Madra helvacea, Chemn. Conch. Cab. vol. vi. p. 234, pi. 23, f. 232, 233.— 

 Lam. Anim. s. Vert. (ed. Desh.) vol. vi. p. 99.— Philippi, 

 Moll. Sicil. vol. i. p. 10, and vol. ii. p. 9. — Chenu, 111. 

 Conch. Mactra, pi. 2, f. 4. 

 „ (jlauca, Gmelin, Syst. Nat. p. 3260. — Do.mov. Brit. Shells, vol. iv. pi. 

 125. — Mont. Test. Brit. p. 571. — Linn. Trans, vol. viii. p. 

 68. — Dorset Catal. p. 68. — Turt. Conch. Diction, p. 80. — 

 TuRT. Dithyra Brit. pp. 73, 258. — Flem. Brit. Anim. p. 

 428.— Brit. Marine Conch, p. 48.— Brown, 111. Conch. G.B. 

 p. 107, pi. 41, f. 1. — Spengler, Skrivt. Natur. Selskab. vol. 

 v. pt. 2, pi. 3. — DiLLW. Recent Shells, vol. i. p. 144. — Index 

 Testae, pi. 6, Mactra, f. 30.— Hanl. Recent Shells, p. 29, 

 pi. 6, Mactra, f. 30. 

 „ Neapolitana, Poli, Test. Sicil. vol. i. pi. 18, f. 1, 2, 3. 

 Encyclop. Methodique, Vers, pi. 256, f. 1. 



This fine Mactra very closely resembles the preceding in 

 its general aspect and features. Its contour ranges from 

 simply oval to ovato-trigonal ; it is by no means solid, is 

 inequilateral, semipellucid, and though decidedly convex, 

 is, for its size, comparatively compressed. The convexity 

 gradually, and nearly equably, diminishes on either side, 

 from the subumbonal region ; the hinder dorsal area is 

 flattened in the adult, but there is no pecuHar angulation 

 at the umbonal ridge, which is occasionally wrinkled con- 

 centrically in the full-grown examples. The entire surface 

 is free from grooves or striae, being smooth, more or less 

 glossy, and of a pale fulvous or light rufous, adorned all 

 over with numerous, and not very broad rays of a rufous 

 or livid rufous hue, with which colouring the dorsal areas 



