ACEPHALA. 393 
Macrra Faucata (Gould). 
Testa magna, transversa, ovato-trigona, inequilaterahs, convextuscula, 
modicé hians, albida, epidermide fulvo, nitido, concentrice rugoso in- 
duta ; umbonibus acutis, approximatis ; latere antico acuminato ; latere 
siphonali late rotundato, sub-truncato ; margine dorsal recto ; area 
dorsali planulata, lanceolata ; margine ventral leniter arcuato: area 
cardinalis ampla ; fossa ligamenta magna, dente V-formi parvo, 
crasso ; dentibus lateralibus compressis, quorum antico valve dextre 
bilobato : interior lactea ; sinu siphonali angusto, elongato, spatulato. 
Mactra falcata, Goutp; Proceed. Boston Soc. Nat. Hist., i. 216. 
May 1850. Expedition Shells, 76. 
Suet large, solid, transversely ovate-triangular, subfalcate, inequi- 
lateral, hinder end short, moderately gaping, white, covered with a 
thick, shining, dusky, straw-coloured epidermis; surface delicately 
marked by incremental lines, with obscure distant radiating ridges; 
beaks acute, nearly touching, post median, rather compressed ; ante- 
rior end narrower than posterior, triangular, somewhat ascendant, 
extremity rather acute; posterior end broadly rounded, truncate at 
tip, in young specimens more triangular ; basal edge regularly arcuate ; 
anterior dorsal edge rectilinear, presenting a plane lanceolate space in 
front of the beaks; posterior dorsal edge rounded, with a coarse, loose, 
dusky epidermis. Valves slightly convex; within milk-white ; sipho- 
nal sinus reaching as far as the beak. Cardinal area large ; ligamentary 
pit large, oblique, shallow; sides of V-tooth very unequal, strong ; 
lateral teeth thin, elevated, anterior one of left valve bilobate. 
Length three and three-fourths inches; height two and a half 
inches ; breadth an inch and an eighth. 
Inhabits the Northwest Coast, Puget Sound. 
This fine species compares best with M. Brasihana, and M. ovals, 
but it is much more inequilateral, and much more broadly obtuse pos- 
teriorly than either of them. Its external characters correspond closely 
with the former, while the narrower siphonal sinus and the hinge 
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