ACEPHALA. 385 
tus ; linea palleali angustd, crenata ; sinu stphonalt profundo, arcuato ; 
cicatrice antertort elongato, falciform. 
Mya precisa, Goutp; Proceed. Boston Soc. Nat. Hist., i. 215. 
May 1850. Expedition Shells, 75. 
SHELL transversely ovate, narrowing backwards, broadly rounded 
anteriorly, where it is widely open, with the lips expanded ; umbonal 
slope full and somewhat angular ; base nearly direct; beaks prominent, 
oblique, incumbent ; epidermis cinereous, wrinkled, thin; tooth large, 
its anterior edge nearly vertical, broader at base than its height, 
rounded posteriorly, so as on the whole to form a quadrant; siphonal 
sinus broad, passing rather beyond the beak, rounded ; pallial impres- 
sion narrow, crenate ; anterior cicatrix very long, falciform. 
Length two and a half inches; breadth one inch; height an inch 
and three-fourths. 
Inhabits Puget Sound, Oregon. 
Differs from M. truncata in being more narrowed posteriorly, more 
rounded anteriorly, more inflated at the umbonal slope, in its narrow 
pallial impression and deeper siphonal sinus, and more particularly in 
having the tooth slope backwards. 
Figures 498, 498 a, lateral and dorsal views of the shell; 498 3, view 
of the interior. 
PANOP#A GENEROSA (Gould). 
Testa magna, ponderosa, calcarea, sub-quadrilateralis, concentrice undu- 
loso-plicosa, epidermide rugoso flavido induta, antice rotundata, pos- 
tacé truncata et valde hians ; umbonibus submedianis, acutis, elevatis, 
undulatis : cardo gracils, dente elevato oblique triangulari instructus : 
cavositas ad apicem profunda ; cicatrice musculari lato, bené impresso ; 
sinu siphonali minimeé profundo. 
Panopea generosa, GouLp ; Proceed. Boston Soc. Nat. Hist., iii. 215. 
May 1850. Expedition Shells, 75. 
SHELL large and ponderous, chalky white, of a somewhat quadri- 
lateral form, the basal and hinge margins being nearly parallel; the 
97 
