ACEPHALA. 463 
Length an inch and a half; breadth an inch. 
Inhabits the Feejee and Samoa Islands. 
The distinctive character of this shell is the series of denticles, 
about twice as long as broad, around the entire shell, and arranged per- 
pendicularly to the margin, tinged purplish or livid slate-colour. One 
young specimen has no coloured margin, but the peculiar denticles are 
present. 
Figure 576, exterior of an elongated specimen ; 576 a, interior of the 
lower valve of a rounded specimen; 576 0, upper valve of the same. 
OstREA DISCOIDEA (Gould). 
T. subcircularis, planulata, tenuis, purpurea : valva supervor liners crebris 
albidis radiata; valva inferior major, radiatim plicoso-rugosa, colore 
saturatiort: cavositas parva, argentata, purpureo-marginata ; mar- 
gine prope apicem plicoso-crenulato. 
Ostrea discoidea, Goutp; Proceed. Boston Soc. Nat. Hist., 11. 347. 
Dec. 1850. Expedition Shells, 97. 
SHELL small, thin, shining, nearly circular, compressed, purple- 
brown. The upper valve is compact, pretty regularly radiated with 
coarse, rather distant, whitish lines. The lower valve is larger than 
the upper, of a more intense purple colour, and corrugated with small, 
interrupted radiating folds. The area near the beaks, by which it 
adheres, is very small. The cavity within is very small and shallow, 
light leaden-colour, with bright, silvery reflections, the surrounding 
limb broad, pure white, and the margin of the lower, which projects 
beyond the upper valve, is purple. Muscular scar transversely elon- 
gated, and very narrow. Hinge delicate, the margins of the valves on 
each side crenulated with fine, transverse folds, sometimes broken up 
into granules for about one-third the circumference. 
Leneth an inch and a half; breadth two inches. 
Habitat unknown. (Sey of Lslonds New Ze and, according fs abe/ 
On type — 4avo) 
