TRIBE MYARIA. 21 
pellucid, smooth ; pearly within, and the hinge with an oblique, 
shallow, spoon-shaped tooth. ?..1.—Brazil.* 
A. Rugosa. Lam. 7. Shape square with the angles rounded 
off, convex, thin, pellucid, obliquely wrinkled.—St. Domingo. 
Rather smaller than the last, and the teeth less isolated. 
A. Imperrecta. Lam. 8. Ovate, scarcely equivalve, the ante- 
* Deshayes makes this species the type of PerrpLroma Schu- 
macher, which is thus characterised. Oval, very inequivalve and 
extremely inequilateral, one side short, subtruncated and but 
slightly gaping : hinge in each valve with a straight and oblique 
spoon-like tooth, forming with the upper margin a deep slope, in 
which is locked a small triangular shelly substance, which adheres 
by a portion of the ligament: muscular impression of the trun- 
cated end very straight and marginal, of the other extremity very 
small and rounded. 
P. Lenticutaris. Sow. Z. P. 1834. Elliptical, lenticular, 
eequivalve, white, dull, thin: epidermis very thin: posterior dorsal 
edge sinuated and forming an angle with the posterior margin. 
41. .=,.—Isle of Muerta. 
P. Arcentaria. Conr. Journ. A. N.S. 7. p. 238. t. 18. f. 8. 
Elliptical, anterior side short, subangulated, slightly reflected, ex- 
tremity nearly direct, truncated ; beaks rather prominent : apophysis 
produced, very oblique ; nacre silvery. 2.—U. California. 
P. PLanruscuta. Sow. Z. P. 1834. Oblong, flattish, ineequi- 
valve, whitish, dull, thinnish: the posterior side short, somewhat 
wrinkled, subtruncated and somewhat sloping at its edge: dorsal 
edge straightish : epidermis thin and palish. 12..22.—W. Co- 
lumbia. 
A. Myalis, Lam. 9, belongs to Leach’s genus 
THRACIA. 
Oval oblong, subequilateral, inequivalve, slightly gaping at each 
extremity. Hinge consisting of a more or iess prominent hori- 
zontal spoon-shaped tooth, which receives the ligament. Palleal 
scar deeply impressed. 
T. Puspescens.* Blainv.—Mya Decuivis. part. D. p.43.— 
W.t. 2. f.4.— Wood. G. C. t. 18. f. 2.—Anatina P. Turt. B. 
(young) t. 4. f. 3.—A. Myauis. Lam, 9.— Kiener Thracia, t. 2. 
f- 2. Ovate oblong, subventricose, inequivalve, subequilateral, ashy 
white, posteriorly rounded, anteriorly subtruncated and angulated : 
hinge furnished with a spoon-shaped process in each valve, whose 
cavity is divided by a single tooth or ridge. 2}..33—W. Europe. 
T. Purcata. Desh. E. vol. 3. p. 1039.—Kiener Thracia, p. 6. 
t.2. f. 3. (bad)—Reeve. t. 35. f. 2. Ovate-oblong, transverse, 
