216 TESTACEOUS MOLLUSCA. 
brown and obscurely rayed; beaks undulated, nacre pearly-white 
and irridescent. 21..3}.— China. 
A. BenepictTensis. Jea.—Sympuonota B. Lea. in Am. 
Ph. Tr. 1837. t. 16. f: 48. Trapezoidal, transverse, inequilateral, 
rather compressed, very thin; dorsal line nearly straight ; forming 
an obtuse angle at each extremity, ventral edge scarcely arcuated ; 
beaks somewhat prominent and granulated at the tip; cuticle shin- 
ing yellowish olive; nacre bluish white and irridescent, scars scarcely 
perceptible, 21..33.—Lake Champlain. 
A. Nurrauiana. Lea.on U. 2. p.77.t. 20. f. 62. Winged, 
elliptical, flattened on the side and enlarged on the umbonal slope, 
ventral edge subincurved ; inequilateral, smooth, thin: beaks com- 
pressed and undulated at the tip: umbonal slope furnished with 
several impressed lines : cuticle smooth, polished, having a dark 
broad band at the line of growth near the margin: nacre white. 
13, .. 253) 
Non-SympepHonote.—A. Oval. 
A. Cyanea.* Lam. 1.—Myrtinus C. Lin. 1158.—D. p. 
315.— W. t. 12. f. 32. Oval, tumid, rounder and ventricose pos- 
teriorly, compressed and more or less angular anteriorly, cuticle 
olive green; in the young the anterior slope is more dilated and 
compressed.— Variety 1. Myr. Ceiuensis. Schre. t. 2.f. 1.— 
A. Sutcata. Lam. 3.— Turt. Man.t. 1. f. 8. Large, ovate- 
oblong, very ventricose, thin, brittle, rather produced anteriorly, 
upper and lower edges nearly parallel and straight.— Variety 2. 
Very like the last; but shorter and the lower edge rather more 
rounded.— Variety 3. Pen. 4. t. 67. f.78. Very like the two 
former, but shorter and the lower edge still more rounded.— Variety 
4, <A. Piscinauis. Drap. t. 12. f.2. Moderate, rather rhombic- 
oval, ventricose, rather thick, often beautifully coloured, produced 
anteriorly with the wing more compressed and elevated.— Variety 
5. Rossm. t. 20. f. 284. Moderate, oblong, rather rhombic, 
rather compressed, brownish, much produced anteriorly, very short 
and rounded posteriorly.—Variety 6. InrermMepIA. Lam. 10. 
ftoss. t.3.f. 68. Moderate, obovate, obliquely truncated anteriorly, 
compressed, striated, brownish green, and yellow zoned.—Variety 
7. A. PonpERosa. Rossm. 4. t. 20. f. 282. Moderate, ovate, 
rather rhombic, ventricose thick, solid rough, internally white, 
anterior slope subangular and rather truncated at the anterior ex- 
tremity, covered with a calcareous deposit.—Variety 8. Small 
elliptical ovate, brittle, rather produced anteriorly : short and 
rounder posteriorly. 7.—Hurope. 
A. Anatina. Lam. 22.—Myrtizus A. Lin. 1158.—D. p. 
317.—Ch. f. 763. Ovate-oblong, fragile, posteriorly rounded, 
anteriorly subangulated, with unequal transverse grooves; beaks 
