386 MOLLUSCA. 
posterior extremity broadly truncated a very little obliquely, and the 
anterior extremity broadly rounded ; anteriorly it gapes slightly, but 
posteriorly it gapes broadly, and the valves are here somewhat everted. 
The surface is coarsely undulated concentrically, and covered by an 
obliquely, and somewhat plumosely wrinkled, dirty yellow epidermis. 
The beaks are sharp and prominent, placed near the middle of the 
superior margin; the anterior umbonal slope is tumid, the posterior 
a little compressed. The hinge is rather slender, having a single 
elevated, erect, obliquely triangular tooth in each valve, with a pit 
behind that in the right valve, and a crest-like elevation for the attach- 
ment of the ligament behind them. Ligament external and double. 
Cavity of the beaks profound; muscular and pallial cicatrices broad 
and well impressed; posterior muscular scar but little broader than 
the pallial impressions ; siphonal sinus shallow, small. 
Length six inches; height three inches ; breadth four inches. 
Found on mud-flats at Nisqually and Puget Sound. 
This large species stands by the side of P. Aldrovandi, but is distin- 
guished by the form of its anterior extremity. One specimen measures 
seven and a half inches in length. ‘The animal is noted as protruding 
its siphon a foot in extent. 
Figures 507, 507 a, lateral and dorsal views of the shell; 507 4, out- 
line of the hinge margin. 
PANOP#A ANTARCTICA (Gould). 
1. subquadrata, crassa, alba, rudis, concentricé undata, postice trun- 
cata, anticé angustata et rotundata; margine cardinali erecto, mar- 
gine ventrali arcuato ; umbonibus latis, elevatis, fere medianis : cardo 
dente parvo, conico instructus : sinu pallial lato, arcuato, minimeé um- 
presso ; cicatrice musculart postica, lunatd. 
Panopea antarctica, Goutp; Proceed. Boston Soc. Nat. Hist. i. 
214. May 1840. Expedition Shells, 74. 
SHELL solid, white, approaching to a square form, but a little longer 
than high, slightly curved at base, rather narrowly rounded anteriorly, 
and having above, broad, elevated umbones; the beaks are a little 

