Sea Shells 
of New Zealand 
Plate XII 
No.2 
Plate X 
No. 16 
the sunny North. Full-grown specimens of three inches 
by two lose their golden sheen and are mostly green, the 
interior of the left valve being a palid silvery green. The 
interior of the right valve is much darker, the lower por- 
tion like jade, the upper part, surrounding the round hole, 
being an opaque white thickened callus, adding to the 
strength of the shell. This reinforcement is all the more 
necessary, for the frame of the “window” is not united 
at the top. 
PLACUNANOMIA ZELANDICA (plakous, a thin 
cake; anomia, unequal; New Zealand).—This is also a 
Saddle Oyster or Window shell, very like the Anomia Walt- 
eri, but with a stronger shell, and a much larger hole in 
the right valve. The most important difference between 
them, and which absolutely distinguishes one from the 
other, is the fact that in the Anomia Walteri there are three 
muscle scars in the left valve, whereas in the Placunanomia 
Zelandica there are but two. These scars are to be seen 
almost in the middle line and rather close up to the beak. 
The beard, or foot, as it is often called—though it is not an 
organ of locomotion,—is a calcified plug projecting through 
the large oblong opening and firmly attached to rock or 
other object. Surrounding the hole is an area of thick, 
smooth white callus, strengthening the part, beyond which 
the remaining portion of the right valve is of a light olive 
greenish brown; the interior of the left valve is dark olive 
green, or the colour of greenstone. Externally, the valves 
are radiately ribbed, but not markedly so. The species does 
not appear to be common. During the last two years I 
have only collected one single specimen, which was at- 
tached to the outside of a large Fan mussel from a sand- 
bank in Pilot Bay at Mount Maunganui. 
Found also in the Hauraki Gulf; at Wellington; Shag 
Point; Lyttelton; Foveaux Strait; Stewart Island; The 
Snares, 
ARCA DECUSSATA (arca, an ark; a chest; decuss- 
ata, crossed).—The Noah’s Ark shell, rather a solid elon- 
gated bivalve of a light brown colour, pale or white in the 
middle, rounded at one end, and more or less pointed at 
the other (posterior). The sculpturing is composed of 
fine ribs radiating from the hinges, crossed or decussated 
by fine concentric ribs. The interior is pale purplish brown 
of a rather dingy hue, marked with radiating ribs and pol- 
ished round the margin. In the recent state the external 
surface is covered with long hair-like epidermis, brownish 
black in colour; hence one of the synonyms, barbatia, sig- 
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