270 TESTACEOUS MOLLUSCA. 
P. Fuscus. Klein.—Son. Th. f. 118,9. Orbicular ventricose 
smoth, the upper valve concave at the umbo and rather elevated 
at the sides, the lower valve very convex at the apex and over- 
lapping the other valve at the margin ; ears wide rectangular, stri- 
ated, concave: the ribs fourteen, narrow and nearly square in the 
upper, wider and rounded with smooth interstices in the lower 
valve: blackish or reddish brown, the inside clouded with light 
brown, 31.. 34. 
P. Stnensis. Sow. Th. f. 120,1. and 134. Rounded, ventricose, 
concentrically striated ; light reddish brown, mottled with darker 
brown, white near the umbones; ears concave, striated ; the very 
concave upper valve, with the twelve central ribs, (the lateral are 
small,) quadrate flattened grooved and narrow, the interstices broad 
and concentrically striated ; the ventricose lower valve with the four- 
teen broad rounded ribs grooved obsoletely and longitudinally, the 
interstices narrow and the margin overlapping the other. 2;'5.. 3/5. 
P. Ziczac. Lam. 5. Sow. Th. f. 129. t0133.—Ch. f. 590,1,2.—#. 
t. 207. f.1.—Osrrea Z. Lin. 1144.—D. p. 249(eaxcluding varieties) 
—List. t. 168 ?—Knorr, 2. t. 20. f. 1.—W. t.11. f. 3. Rounded, 
ventricose, smooth, the ears large, rectangular, with one or two 
broad slightly raised ribs on the upper part: upper valve flat, 
with a broad area on each side destitute of ribs; ribs thirty-one, 
depressed, alternate, the interstices narrow and most minutely 
striated : lower valve with twenty-four broad ribs which are obso- 
lete near the umbo and devoid of interstices ; colour variable, the 
under valve generally reddish brown softened into purple or white 
towards the umbones, the upper variegated with white spots, in- 
terrupted rays of brown and ziczac lines. Red Sea and Phillip- 
pines, 3-3,..33. 
P. Denratus. Sow. in Zool. P. 1835.—Sow. Th. f. 49. 
Very inequivalve, equilateral; ears equal ; the valve flattened, with 
radiating sulci and striz; the lower valve very convex, smooth, 
with radiating sulci, the ventral edge deeply toothed : edge of the 
upper valve falling deeply within. 32..33. W. Colombia. 
P. Erytur#ensis. Sow. Th. f. 163,4. Rounded, ventricose, 
smooth; auricles concave and large; upper valve concave, with 
nine central ribs, which are concave and distant, three smaller 
ones on each side; lower valve (which overlaps the other at the 
margin) with twelve rounded, broad ribs; yellowish white varie- 
gated with red, the umbones stained with purple: inside purplish 
brown. 2...254,. Red Sea. 
P. Pyxipatus. Born. t. 6. f. 5.6.—Sow. Th. f. 24,5.—D. p. 
268.—Osrrea Sutcata. Gmel.—Ch. f. 604. Inequivalve, or- 
bicular; the ears large and nearly equal, with several fine coste ; 
upper valve flat, hollowed near the umbones, with twenty-two ribs 
