APPENDIX. 373 
with chocolate on the subnodulous and concave umbonal slope, closely 
fimbriated by gradate concentric ridges, that are decussated by still 
more dense radiating lyre; umbonal ridge angular ; beaks pointed, 
seated near the end of the tawny-brown ligament, which is elongated 
and broadish; inside white, stained with chocolate in front, and on 
the hinge-margin; teeth numerous. 12. Pacific. The ventral 
edge is usually incurved and slightly gaping. 
Arca Reeveana (t. 18, f. 51, as A. squamosa, vaR.), D’Orb. Am. 
for A. Hersuinen, Reeve, Ic. (not Brug.). Equivalve, subrhombic- 
oval, compressed, moderately thick, subinequilateral, white, with a 
rich brown shining somewhat scaly epidermis, roughened throughout 
by very numerous radiating costelle, that are crowded and not much 
raised in the middle of the shell, where they are geniculated by 
the ridge-like wrinkles of increase, and are much more prominent, 
larger and more distant at the sides, where they are closely 
and nodosely crenated. Ventral edge gaping. Beaks seated at, or 
before, the second third of the length of the produced, narrow and 
sunken ligamental area, which is set with groove-like lines that 
diverge in very obtuse angles from the acute and prominent apices. 
Extremities with obtuse angles dorsally, rounded ventrally. Inside 
pure white; teeth very small in the middle, abruptly larger at the 
sides. 12...24. W. America. 
Arca DEcussaTA (t. 19, f.16)—Byssoarca pv. Sow. Z. P. 1833, 
p. 18.—A. p. Reeve, I. Car. f. 81. Equivalve, inequilateral, thick, 
subventricose, oblong or oval-oblong, bluntly angulated dorsally, 
rounded ventrally, white, with an epidermis of dirty brown pointed 
scales; most closely radiated with very narrow costelle, that are 
very closely and minutely decussated, the anterior riblets nodosely 
crenated, their intervals narrow; ventral edge gaping, arcuated ante- 
riorly; ligament produced, narrow, evenly lanceolate; beaks rather 
acute and projecting; inside wholly white. 14...2. Pacific Isles. 
«= (Area proper). Ventral edge regularly notched or 
; toothed. 
Arca Dinuvir (t. 18, f. 38).—A. anriquara, Phil. (not Lin.) 1, 
p. 59, t. 5, f.2.—A. v. Phil. 2, p.48. Obliquely suboval, equivalve, 
very inequilateral, solid, tumid, white, radiated with nearly 30 rounded 
ribs, which, as well as their nearly equal deep intervals, are closely 
striated concentrically; dorsal edge angulated at each extremity ; 
anterior side with a rounded-off angle at the notched and arcuated 
ventral edge, which rises obliquely behind; umbones prominent; 
beaks remote; ligamental area tawny-brown, oval-lanceolate, with 
numerous close grooves that form very obtuse angles: teeth numerous. 
11...1,%. Mediterranean. 
