Mactra. MOLLUSCA. MACTRADiE. 427 
Concha crassa, List Ang. 174. t. iv. f. 24. Conch, t. ccliii. f. 87* — M. sol. 
Penn. 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, ti cxxvi. — M. truncata, Mont Test. 
Brit. Sup. 34. Turt Biv. Brit. 68. — Sandy coasts, rare. 
Length 1|, 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 being raised in the middle, and by the front 
margin being shorter and more regularly semicircular. 
446. M. subtruncata. — Shell sub triangular, 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 x^^ths, breadth T^ths 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 abruptly 
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, flattish, inequilateral, 
rounded at the elongated side, and somewhat truncate at the 
other, with the beaks incurved.” 
Turt Biv. Brit. 71* t. v. f. 8. — “ Dredged up in the offing of Exmouth.” 
“ Shell |ths of an inch long, and l^th of an inch broad, 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.^ shell fragile. 
448. M. stultorum. — Shell subtriangular, slightly depressed 
from the beaks at each extremity ; finely striated transversely, 
with pale longitudinal rays. 
Linn. Syst. i. 1126 — Tellina radiata, Penn. Brit. Zool. iv. 87. t. xlix. 
f. 30. — M. stult. Mont Test. Brit. 94. Don. 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 strise 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 prominent and compressed ; 
beaks nearly central, and, together with the inside, purplish. 
