312 TESTACEOUS MOLLUSCA. 
on one or both sides (in characteristic examples saddle-shaped) ; 
rather thick, purple: the hinge-ridges of nearly equal length, not 
longer than they are separate from each other at the base. 5. 
Java, &e. 
P. PapyRACEA.—PLACENTA QUADRANGULA, Retz, from Gualt. t.104, 
f.B.—Epuirrivum, &e., P., Ch. f.715, copied FE, t.174, f. 2.—ANoMIA 
SELLA, JuNIor, D. p. 297.—P. P., Lam. 2.—Gray, Cat. Plac. p. 2. 
Somewhat quadrilateral, nearly flat, thin, hyaline, brownish purple, 
or subradiatingly mottled with purplish liver-colour and white; 
hinge as in the last species. 4. Red Sea. Perchance the young of 
SELLA. 
P. Puacenra.—Anomia P., Lin. 1154.—Ch. f. 716.—D. p. 297.— 
W. t. 12, f. 29.—Piacenta OrBicuLaRis, Retz. p. 15.—Gray, Cat. 
Plac. 4.—P. P., Lam. 3.—E. t. 178, f. 8—Crouch, t. 12, f. 11.— 
Reeve, CO. S. t. 122.—Woodw. t. 16, f. 6. Suborbicular, longer than 
broad, becoming narrower towards the hinge, white, semitransparent, 
not flexuous: ridges of the hinge very gradually diverging from each 
other, of very unequal length; scar not directly under the middle of 
the hinge. 6. China. 
P. Lincornu. Gray, Cat. Plac. 3. Flat, rather solid, subopaque ; 
outline suborbicular, rounder before and behind: ridges of the hinge 
elongated, nearly equal, longer than they are separate from each 
other at the base, their angle not acute. Australia. 

ANOMIA. 
Inequivalve, irregular, attached by a plug, more or less nacreous 
within: under valve with a large perforation near the umbo: upper 
valves with 2 or 3 subcentral muscular impressions. 
* Upper valve with 3 subcentral muscular scars. 
A. Epurppium. Lin. 1150.—Lam. 1.—Turt. Biv. 227, pl. 18, 
f. 1, 2, 3.—Br. Mol. 2, p. 325, pl. 55, f. 2, 3, 6, 7.—A. Cupa, 
Lin. 1151.—Poli, t. 30, f..1, 2, 5 to 8—Lam. 3.—Turt. Biv. 228, 
t. 18, f.4.—A. Execrrica, Lin. 1150.—Lam. 4.—Turt. Biv. p. 226, 
t. 17, f. 8, 9.—A. Squamura, Lin. 1150.—Lam. 8.—Turt. Biv. 229, 
t. 18, f. 5, 6, 7.—A. Puncrata, Ch.—Turt. Biv. pl. 18, f. 11-— 
A. Viotacea, Cucunuata, Brug. 70, 71.—A. FLExuosa, Ruaosa, 
Cyninprica, Gm.—A. Maraariracea, Poli.—A. PaTe.iaris, Pyrti- 
ForMIs, Fornicata, Lam. 2, 5, 6.—A. Cympirormis, Mat. and Rac. 
—A. Tupuxaris, Turt.— A. Coronata, Bean.— A. PotyMorpPHa, 
ScaBreLuA, Phil. Moderately strong when mature, of very variable 
contour, suborbicular in freely-developed examples, smooth, or with 
slight concentric wrinkles (occasionally, from being moulded upon 
