284 GINGLYMACONCHA. MACTRADZ. 
Genus 32. MactTrRa. 
The shell trigonal, rounded behind and beneath ; the hinge 
with one angulated tooth in each valve; in one valve it is 
entire, in the other broken; and with a lamella before and be- 
hind the cardinal tooth, in one valve simple, in the other dupli- 
cated. 
The tracheal tubes elongated, equal, and equally broad. 
1. Mactrra STULTORUM. 
Shells smooth, striolated concentrically ; the epidermis grey 
or rufous brown, rayed with pale whitish rays of the same 
colours. 
Colour pale reddish-brown, grey or white, sometimes tinted 
with purple; inside white, occasionally spotted or coloured 
with pale purple. Length two inches; height one and a half. 
Mactra Stultorum, Linn. Syst. Nat. i. 1126; Penn. Brit. 
Zool. iv. 92; Mont. Test. Brit. i. 94; M. & R. Trans. 
finn. Soc. viii. 69; Flem. Ent. Encycl. vii. 93 ; Dill. Dese. 
Cat. 138; Lam. Hist. Nat. des Anim. sans Vert.; Turt. 
Conch. Dict. 81. 
Tellina depressa, Penn. Brit. Zool. iv. 87. t. 49. f. 30, junior. 
Mactra cinerea, Mont. Test. Brit. Supp. 35. 
Mactra Stultorum, var., Turt. Conch. Dict. 81. 
Inhabits most of the sandy shores of Britain, and is very 
common. ‘The second variety differs from the first, merely in 
wanting the colour of its rays ; its form is absolutely the same. 
The third variety was discovered by the present Provost of 
Eton, at Barmouth in Wales, in company with the first variety 
and nearly in equal abundance. Since then I have found this 
variety full-grown at Hastings, in great abundance. 
2. MACTRA SUBTRUNCATA. 
Shells abruptly produced behind and concentrically ridged ; 
the ridges numerous, nearly equal in size, and set close to one 
another ; abruptly produced. behind. 
