396 MOLLUSCA. 
rather more elevated than usual, compressed. Interior chalky white, 
polished at the margin. Siphonal sinus linguiform, extending half 
the length of the shell. 
Length five and three-fourths inches; height four inches; breadth 
three inches. 
Inhabits Puget Sound. Dr. Pickering. 
This is an extraordinary shell, and by far the largest species of the 
genus. It proves to have been described previously to the description 
published by me; but as it is a remarkable species, and the work of 
Middendorff not easily accessible, it is reproduced in this work. 
Figure 508, 508 a, lateral and dorsal views of the shell; 508 d, the 
hinge. 
Panpora cisTuLa (Gould). 
Testa solida, alba, valde inequilaterals, falciformis, anticée rotundata, 
postice angustata, truncata: valva plana tenuis, submargaritacea, 
concentrice undulata ; margine dorsal subrecto, late inflecto, dente 
brevi, elevato, trianqulari munito: valva concava solidior, ossea, 
tumida, postice costato-angulata, edentula, fossa ligamentah et costa 
antical instructa ; margine dorsah concavo ; margine ventrali valdé 
arcuato. 
Pandora cistula, Goutp; Proceed. Boston Soc. Nat. Hist., iii. 217. 
May 1850. Expedition Shells, 77. 
SHELL solid, bony, transversely elongate, very inequivalve and in- 
equilateral, falciforrm ; obtusely rounded anteriorly ; gradually narrow- 
ing and strongly recurved posteriorly, and truncated at tip; right 
(flat) valve, thinner than the other and less recurved, the folded, pos- 
terior, dorsal edge, which shuts over the other valve being broad, flat, 
and nearly rectilinear; on the exterior is a submarginal, obtuse ridge ; 
surface somewhat undulate concentrically, sightly pearly outside and 
inside. ‘There is a single short, elevated, triangular tooth, and _poste- 
rior, oblique, ligamentary groove. Left (concave) valve much more 
solid, bony, and dead white, the posterior umbonal slope tumid; the 
