174 OSTREID&. 
green, internally green; upper scar large oblong; lower scars two, 
large, rather smaller than the upper one, close together but not 
confluent, the lowest one the largest (Gray). 
Stewart Island. Peru. 
A doubtful determination. 
A. cyteum, Gray, P.Z.S, 1849, p. 115. Shell sub-orbicular 
smooth ; internally reddish, upper muscular scar very large, sub-cordate; 
lower two, sub-orbicular, smaller, nearly equal sized; the upper in the 
notch of the upper (sic.) one; the lower hinder close to lower hinder‘ 
edge of the upper one ; sinus in lower valve large (Gray). 
Stewart Island. China. 
A very doubtful determination. _ 
Genus, PLACUNANOMIA—Broderip. 
Shell not eared ; upper valve with two sub-central muscular scars ; 
the anterior lobe of the upper notch agglutinated to the cardinal edge ; 
plug shelly at the top and near the body to which it is attached, and 
with horny longitudinal laminve below and internally. 
P. zealandica, Gray, Dief, N.Z., ii., p. 260, Reeve, Conch. Ic, 
YrAsVoynylirebus and Lerner pl. 2.07105 ‘Chen, \fogo84s7) 5Ub- 
orbicular, white, smooth ; upper valve with distant radiating grooves ; 
internally dark green; upper valve with two confluent scars ; upper 
oblong, longitudinal, lower rather small and more transverse ; thin, 
translucent (Gray). 
Stewart Island to Auckland. 
P. ione, Gray, Proc. Zool. Soc., 1849, p. 123; Reeve, Conch. Le., 
jf. 6. White, laminar; edge of the lamine with small, slender, elon- 
gated processes ; interior green ; lower muscular scar small, round, on 
the lower hinder edge of the larger one ; sinus or perforations large 
(Gray). 
Stewart Island. Australia. Tasmania. 
FAMILY—OSTREID. 
Labial appendages triangular, connected round the mouth by a plain 
membrane ; palps separate from the gills. Mantle entirely open, the 
edges double, and each bordered by short tentacular fringes ; no con- 
spicuous ocelli ; branchial leaflets not doubled on themselves. Foot 
obsolete. Shell inequivalve, inequilateral, irregular, close and fixed by 
the inferior valve, which is the largest, or free; beaks central, straight ; 
adductor impression single, behind the centre ; hinge toothless. 
Genus, OSTREA—Linneus. 
Irregular, attached by the left valve ; upper valve flat or concave, 
