Mactra. MOLLUSCA. MACTRAD^. 427 



Concha crassa, List. Ang. 174. t. iv. f. 24. Conch, t. cclili. f. 87« — M. sol. • 

 Peim. Brit. Zool. iv. 92. t. lii. f. 43. Don. Brit. Shells, t. Ixi. Mont. 

 Test. Brit. 92. Turt. Biv. Brit. 67 — Sandy coasts. 

 Length seldom above an inch and three quarters ; breadth upwards of two 

 inches ; yellowish white ; obsoletely striated by the layers of growth, with a 

 few distant concentric furrows ; the beaks are nearly central, and the outline 

 of the anal angle of the shell is slightly irregular ; inside glossy white. 



445. M. truncata. — Shell triangular, depressed from the 

 beaks at both extremities ; equilateral. 



M. subtruncata, Don. Brit. Shells, t. cxxvi. — M. truncata, Mcmt. Test. 

 Brit. Sup. 34. Turt. Biv. Brit. 68.— Sandy coasts, rare. 

 Length H, breadth l|th inches; yellowish-white ; irregularly striated by 

 the layers of growth. It is readily distinguished from the preceding by the 

 greater convexity of the valves, and prominence of the beaks ; by the depres- 

 sions on the extremities not beuig raised in the middle, and by the front 

 margin being shorter and more regularly semicircular. 



446. M. subtruncata. — Shell subtriangular, inequilateral, con- 

 centrically striated. 



(Trigonella subtruncata Da Costa, p. 198.)— M. stultorum, Penn. Brit. 



Zool. iv. 92. t. lii. f. 42.— M. subtruncata, Mont. Test. Brit. 93. Turt. 



Biv. Brit. 70.— Sandy shores, common. 



Length /sths, breadth /gths of an inch. This species is distinguished from 



the two preceding, by the regularity of its concentric striae ; by the front 



margin being straighter towards the more produced anal, and more abi-uptly 



curved at the oral angle ; the syphon marks are less distinct ; it resembles the 



M. solida in the mesial prominence of the depressions at both sides of the 



beak. 



447. M. deaurata. — " Shell oblong, fiattish, inequilateral, 

 rounded at the elongated side, and somewhat truncate at the 

 other, with the beaks incurved." 



Turt. Biv. Brit. 71- 1. v. £ 8. — " Dredged up in the ofRng of Exmouth." 

 " Shell |ths of an inch long, and lith of an inch bi-oad, opaque and strong ; 

 one side elongated, sloping from the beaks, and rounded ; the other shorter, 

 and somewhat angular, where it is a little open ; colour dull greyish-white, 

 covered with a shining bronzed skin, reflecting metallic lustres ; coarsely and 

 irregularly striate transversely, with a few coarser ridges towards the hinge ; 

 inside glossy, greyish white, with the margin plain ; beaks rather prominent 

 and pointed, a little inclining to the longer side." 



* Lateral teeth smooth, shelljragile. 



448. M. stultorum. — Shell subtriangular, shghtly depressed 

 from the beaks at each extremity ; finely striated transversely, 

 with pale longitudinal rays. 



Unn. Syst. i. 1126 — Tellina radiata, Penn. Brit. Zool. iv. 87- t. xlix. 



f. 30 — M. stult. Mont. Test. Brit. 94. Drni. Brit. Shells, t. cvi. Turt. 



Biv. Brit. 72 — Sandy coasts, common. 



Length about 2, breadth about 2^ inches ; shell thin, with a fine brownish 



cuticle ; the striae at the anal angle are rough, from which to the beak the 



depression has an obtuse mesial prominence ; the depression at the opposite 



extremity is less distinct, and the mesial more jn-ominent and compressed ; 



beaks nearly central, and, together with the inside, purplish. 



