TRIBE MACTRACEA. 33 
M. Execans. Sow. Tank. Cat. t. 1. f. 3.—Desh. in Lam. 6. 
p- 107. Rounded triangular, the hinge margin nearly forming a right 
angle at the beak, whilst the ventral margin is all but a semicircle, 
tumid, thin, anterior slope sharply carinated; yellowish white, with 
rounded concentric grooves: lateral teeth short small and approxi- 
mate.— Florida. A more rounded and tumid shell than Plicataria. 
M. Virrea. Gray. Mag. N. A. 1837. Oblong trigonal, thin, 
white, pellucid, umbones incurved, sub-anterior; posterior slope 
flattened, edge waved: anterior slope compressed, its depression 
elongated, with a slight riblike raised edge ; lunule depressed, lan- 
ceolate : lateral teeth short, very small, and very approximate. 1{. 
M. Cyanea. Chem. f. 207.—D. p. 134.—M. Cyenus. Gimel. 
3260.— W. t. 6. f. 6. Ovate triangular, ventricose, slightly wrinkled 
transversely, solid, whitish, and anteriorly obliquely truncated : the 
posterior slope heart-shaped and finely striated : umbones close : 
lateral teeth smooth. 14.— China. 
M. Exoueta. Gray. Mag. N. H. 1837. Trigonal, white, 
thin, pellucid, slightly striated concentrically, covered with thin 
pale periostraca ; posterior slope compressed, produced, anterior 
slope ventricose, flattened, edged with a slightly raised keel: ante- 
rior lateral teeth very small and close, the posterior one elongated.— 
Cape Horn. 
M. Discors. Gray. Mag. N. H. 1837. Ovate, trigonal, 
rather solid, ventricose, white ; umbones nearly close, with two 
diverging reddish lines ; anterior depression rather flattened, rugu- 
lose, margined by slightly raised lines, with two or three raised con- 
centric ones: lunule concentrically grooved : lozenge, smooth ; lateral 
teeth subequal and moderately distant. 
M. Rerevesu. Gray. Mag. N. H. 1837. Wedge-shaped, 
thin, white, pellucid, striated concentrically : curved near the umbo: 
lateral teeth subequal, rather long and approximate: hinge margin 
two-edged.— China. 
M. Exroneata. Quoy. Ast. t. Ff.  Oblong-ovate, rather 
solid, smooth pale brown, covered with a rather thin olive epidermis : 
anterior slope slightly rugulose: lateral teeth close, rather short, 
the posterior one notched, the other sub-triangular. 13.—New 
Zealand. 
M. Simruis. Gray. in W.S.t. 1. f. 5.—Spisura 8. Gray. 
Mag. Nat. H. 1837.—Beech. Z. t. 44. f.8.—M. Ovauts. Gould. 
p. 532 (fide Gould.) Oblong-ovate, rather thin, pale reddish 
white under an olive epidermis: anterior slope slightly indicated : 
lateral teeth short, triangular, close. 2..3.—Van Diemen’s Land. 
M. Aspersa. Sow. Tank. Cat.—M. Tenera. W.S.t. 1. f. 
4. Oblong, compressed, inequilateral, rather solid, smooth, but 
slightly rugulose on the anterior slope, and the posterior concen- 
trically grooved ; white, speckled with dark chesnut. 2. 
D 
