. The edible clams, mussels and scallops of California. — 11 — ee. Siphons short or moderate, a pallial sinus present; burrowing more or less deeply, f. Size small, valves crenulate or toothed on inner surface of margins, teeth interlocking in closed shell; siphons separate; pallial sinus reaching about half way from posterior to anterior muscle scar. Wedge shells Donax g. Umbo central. D. californica p. 47; pi. 16, fig. 1 gg. Umbo much nearer posterior end. D. laevigata p. 47 ; pi. 16 , fig. 2 ff. Size moderate or large, valves usually smooth at margins, sometimes roughened but without regula
. The edible clams, mussels and scallops of California. — 11 — ee. Siphons short or moderate, a pallial sinus present; burrowing more or less deeply, f. Size small, valves crenulate or toothed on inner surface of margins, teeth interlocking in closed shell; siphons separate; pallial sinus reaching about half way from posterior to anterior muscle scar. Wedge shells Donax g. Umbo central. D. californica p. 47; pi. 16, fig. 1 gg. Umbo much nearer posterior end. D. laevigata p. 47 ; pi. 16 , fig. 2 ff. Size moderate or large, valves usually smooth at margins, sometimes roughened but without regular crenulations; siphons united. g. Pallial sinus deep, reaching more than half way to anterior muscle scar. (See Fig. 9; compare with Fig. 10.) h. Valves with radiating ribs. Paphia 1. Fig. 9. Paphia stami- nea. One-half natural size. Fig. 10. Tivela stultorum. half natural size. One- i. Valves about round in outline, ribs prominent, concentric ridges faint; pallial sinus reaching somewhat more than half way to anterior scar ; valve margins roughened. Rock cockle P. staminea p. 38 ; pi. 10 , fig. 2 ii. Valves elongated, ribs small but distinct, concentric ridges more prominent than ribs ; pallial sinus reaching | of distance to anterior muscle scar; valve margin smooth. Thin-shelled cockle P. tenerrima p. 38; pi. 10 , fig. 1 hh. Valves without radiating ribs, concentric ridges distinct; pallial sinus reaching § of distance to anterior muscle scar. Washington clams Saxidomus i. Concentric ridges bold and prominent. S. nuttalli ii. Concentric ridges finer and less conspicuous. S. giganteus p. 35 ; pi. 7 , figs. 1, 2 p. 35 ; pi. 8 , figs. 1, 2 jg. Pallial sinus small, reaching not more than half way to anterior muscle scar. (See Fig. 10.) h. Ligament external, valves heavy with moderate or thick edges, i. Valves smooth, very heavy, with marked glossy, persistent perios- tracum; pallial sinus reaching less than one-third way to anterior muscle scar ; found in clear sand on ope
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