Mactba. MOLLUSCA. MACTHAD^. 427 



Concha crassa, List. Ang. 174. t. iv. f. 24. Conch, t. ccliii. f. 87- — M. sol. 

 Penn. Brit. Zool. iv. 92. t. Hi. f. 43. Don. Brit. Shells, t. Ixi. Mont. 

 Test. Brit. 92. Turt. Biv. Brit. G^ — 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, Mont. Test. 

 Brit. Sup. 34. Turt. Biv. Brit. G8. — Sandy coasts, rare. 



Length 1a, breadth If th inches; yellowish-white ; irregularly striated \>y 

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

 greater convexity of the valves, and prominence of the beaks ; bv 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 subtriangular, inequilateral, con- 

 centrically striated. 



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

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

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



Length T 6 „ths, breadth T 8 c ths of an inch. This species is distinguished from 

 the two preceding, by the regularity of its concentric strise ; 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. soUda 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.' 1 



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 metalHc 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 Httle 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. 112G — TelHna 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 2i 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. 



