288 MALACOZOA. TROPlOPODA. LAMELLIBRANCfllATA, 



The adductor muscles large, the anterior above and before the 

 mouth, the posterior below the rectum, both submarginal. 



Common along the sandy coast, and frequently cast on 

 shore alive. 



Mactra stultorum. Linn. Syst. Nat. i. 1126. Tellina radiata. 

 Penn. Brit. Zool. iv. 87. PI. 49. f. 80. Mactra stultorum. Mont. 

 Test. Brit. 94. Mactra cinerea. Mont. Test. Brit, Suppl. 35. 

 Mactra stultorum. Penn. Brit. Zool. Ed. ri. iv. 193. PI. 52. f. 1. 

 Mactra cinerea. Penn. Brit. Zool. Ed. n. iv. 196. Mactra stul- 

 torum. TurtBrit. Biv. 72. Mactra cinerea. Turk Brit. Biv. 73.- 

 Mactra stultorum. Flem. Brit. Anim. 427. Mactra stultorum. 

 Lamk. Syst. v. 474; Ed. n. vi. 99. 



2. Mactra solida. Thick-Shelled Mactra. 



Shell subtrigonal, ovato-trigonal, or subelliptical, very 

 thick, smoothish, the concentric striae being obsolete, but sub- 

 antiquated, with strongly marked growth-lines, white, more 

 or less tinged with grey or reddish, the umbones prominent, 

 recurved, nearer the anterior end ; the anterior slope more 

 abrupt ; the internal surface dull white, the margin and very 

 deep muscular impressions glossy greyish-white. Length two 

 inches and a-half, height two inches. 



Individuals vary in form. Generally the young shells are 

 elliptical, but not so thin as to be partially diaphanous, like 

 those of Mactra elliptica. Very old shells are almost as high 

 as long, and extremely thick. Some are more triangular than 

 others; some have the umbones nearly central, others have 

 the anterior slope much shorter. When long exposed on the 

 beach, the shells become banded with bluish or reddish. 



Common along the sandy coast, and frequently cast on 

 shore. 



Mactra solida. Linn. Syst. Nat. i. 1 126. Mactra solida. Penn. 

 Brit. Zool. iv. 92. PL 51. f. 43. A. PI. 52. f. 43. Mactra solida. 

 Mont Test. Brit. 92. Mactra solida. Turt. Brit. Biv. 67. Mac- 

 tra solida. Flem. Brit. Anim. 426. Mactra solida. Lamk. Syst. v. 

 477 ; Ed. n. vi. 104. 



3. Mactra elliptica. Elliptical Mactra. 



Shell subelliptical, very thin, subpellucid, smoothish, some- 

 what glossed, with faint and very delicate concentric striae, 

 moderately conspicuous growth-lines, and slight indications of 

 radiating striulae ; umbones prominent, pointed, recurved, 

 nearly central ; the anterior slope convex, the posterior less 

 o, and forming an obtuse angle with the arched inferior mar- 



