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726 APPENDIX 1 ei 
mities rounded; ligament margin very oblique, slightly arcuate; basal margin arcuate. 
Beaks near the anterior extremity.—Plate 18, figs. 6, 6 a. iz he 
Astoria, Oregon. % 
Nucuia rmpressa (Conrad).—Oblong ovate, convex, with regular concentric irn- 2 
pressed lines. Anterior extremity rostrate, slightly recurved, extremity truncated ; liga- 
ment margin arcuate, slightly declining; rounded behind. Beaks submedial. Basal 
margin arcuate, slightly contracted near the anterior extremity.—Plate 18, fig. 7 a, 6, 
Cy dane: 
Astoria, Oregon. 
[Length 1 inch; breadth very nearly half an inch. Apical angle 155° to 160°. The 
fine lines of the surface are neat, but closely crowded. ] 
PrecruncuLus patuLus (Conrad).—Suborbicular, convex, with radiating lines. Hinge 
margin elongate. Extremities rounded; anterior margin curved inwards ; posterior mar- 
gin, nearly direct.—Plate 18, fig. 8, 8 a, natural size. 
Astoria, Oregon. 
{Length 13 inches ; height about 12 inches.] 
Pecruncutus nitEeNns (Conrad.)—Suborbicular, oblique, smooth and polished, with — 
fine obsolete radiating lines, extremely neat. Hinge margin quite short, rectilinear ; pos- 
terior margin slightly arcuate-—Plate 18, fig. 9, a, 6, natural size. 
Astoria, Oregon. 
[Length 3 inch; height {885 L.] 
Arca pevincra (Conrad).—Rhomboidal. Ribs narrow, flattened, and little prominent 
anteriorly; on the posterior side wider, slightly convex, and longitudinally striated. 
Beaks distant.—Plate 18, figs. 10, 10 a. en 
Astoria, Oregon. 
Arca ———. A cast having a rhomboidal outline, with prominent distant beaks. 
Plate 18, fig. 11 a, 0. 
Carpita sustentA (Conrad).—Not longer than high, broad obovate, ventricose, 
with about twenty-two rounded, not very prominent radiate coste, and with strong con- 
centric wrinkled lines. Posterior extremity somewhat truncate.—Plate 18, figs. 12,12 a. ‘ 
Astoria, Oregon. 
[Length and height $ inch; thickness ? inch; apical angle 105°.] 
PrctEeN propatuLus (Conrad).— Large, subequivalve, suborbicular, compressed ; 
coste about 17, rounded, narrow, interstices much wider than the ribs; ears unequal. 
Plate 18, fig. 13, 13 a. 
Astoria, Oregon. 
[Length and height 4 inches.] 
TEREBRATULA NITENS (Conrad).—Ovate, smooth and glossy. Superior valve con- 
vex; inferior valve flattened towards the base; basal margin sinuous; beak prominent, 
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