TESTACEOUS MOLLUSCA. 275 
compressed, subequilateral; pellucid, very thin, smooth; ears 
small, obtusely angulated, the posterior the smaller: lower valve 
covered with avery thin opaque lamina. 1..1. Greenland. 
P. Lariauritus. Conrad. in J. Ae. N.S. Phil. 7. (including 
his Mesotimeris ?)—Sow. Th. f. 20,1.—P. Tunica. Phil. Conch. 
Peeten, t. 1. f. 3. Obliquely subquadrate, inequilateral, thin, 
rather flat, anteriorly attenuated ; the ears oblique and costated ; 
umbones posteriorly inclined; brown variegated with ziczac marks 
of white or plain orange, with twelve smooth rounded ribs, the 
interstices concentrically striated. 1555..1. California. 
P, Tumipus.* Turton Biv. t. 17. f. 3.—Sow. Th. f. 27,8,9.— 
Osrrea T. Turt. C. D. p. 132. Orbicular, rather compressed, 
small, thin, smcoth; ears large, nearly equal; either pale fawn 
mottled with red and brown, or white or yellow. 0,22..0,22. 
England. This may prove identical with Similis of Laskey. 
P. Orricuraris. Sow. Th. f. 231,2. Orbicular, inequivalve © 
smooth, thin, nearly equilateral; ears nearly equal; upper valve 
ventricose, horn-coloured with a broad submarginal band of dark 
purplish brown and speckled with lighter brown; lower valve 
rather depressed, much lighter, with only light brown speckles ; 
posterior ear very strongly emarginated. 2...2,. Africa. 
P. Hyauinus. Polt, ¢. 28. f. 6.—Philippi. 1, p. 80.—Sow. Th. f, 
66,7,—Orbicular, smooth, hyaline, rather compressed, the sides 
somewhat expanded ; ears large, nearly equal, acutely angulated, 
flat; red with small angulated marks of brown and white arranged 
inrays. Variety. Without spots. 49...1. Mediterranean. 
P. Fracerxatus. | Lam. 16.—Del. t. 16. f. 4,7.—Sow. Th. 
f. 41,2,3. Squarish round-shaped, thin, compressed, nearly 
transparent, irregularly ribbed or striated, horn coloured ; pinkish 
or yellowish at the sides and auricles, with minute angular marks 
of white and brown; ears large and acute. Variety. Blackish 
brown. 5/5..-3. Mediterranean. 
P. Grazer. Ch. f. 642,3.—Lam. 20.—Sow. Th. f. 169 to 
176.—Ostrea G. Lin. 1146.—D: p. 264.—W. t..10. f. 41,— 
Knorr. 2, t. 10. f. 2.— Including P. Vireo? Lam. Orbicular, rather 
flattened, smooth or radiately striated, spreading at the sides; ears 
nearly equal, broad, acutely angulated; extremely variable in 
colouring, in those which are variegated the markings angular 
and defined; ribs ten, rather rounded, slightly raised near the 
umbones, flattened so as almost to disappear near the margin, 
the alternate ones much less elevated. 2...2-1,. Mediterranean. 
P. Discors. Chemnitz. f. 2042. P, Prorgus. Sow. Th. f. 53,4, 
83,4.—Osrrea P. D. p. 265.—W. t. 10. f. 42. Subtriangular, 
compressed, subinequivalve, smooth, or obsoletely striated; ears 
‘ T2 
