margin is quite straight, and gives attachment to the liga- 
ment; the ventral margin, with a large curve outwards 
at the posterior end, merging to concave at the anterior end, 
forming an Ogee, or what Hogarth termed the “line of 
beauty,” especially noticeable in the young shell. The 
sculpture is composed of ribs radiating from the point fan- 
wise, with hollow spines at the broad end. The colour is 
dark brown, inclined to purple, the interior being iridescent 
and shiny. Immature shells, up to about three inches in 
length, are transparent, exceedingly thin and fragile, of a 
pale horn colour or grey. The adult shell attains a length 
of eleven inches. Buried in muddy sand, point down- 
wards, and with from half an inch to several inches of the 
posterior end of the valves exposed, it is found just below 
low water to a depth of twenty fathoms or more. The 
animal spins a beard composed of fine silky filaments, situ- 
ated near the anterior end, and which is attached to numer- 
ous fragments of shell. This mass of broken shell forms 
sufficient anchorage to prevent the mollusc being washed 
out of its bed, and the hollow spines also serve the same 
end. Another interesting point to be observed in the Fan 
mussel is the extreme length of the ligament, necessitated 
by the fragility of the shell; the fragility again giving rise, 
in the inquiring mind, to a curious problem as to whether 
the thinness of the shell causes the animal to bury itself for 
protection, or whether the shells were originally of more 
solid build, and the burying habit of the mussel in the 
course of time brought about this relative thinness. Here 
we are faced with a knotty point, like the owl in Froude’s 
Essays, which acquired an aspect of profound wisdom 
through constantly pondering over the question as to 
whether the first owl came out of an egg, or the first egg 
came out of an owl! 
The Atrina Zelandica is found throughout New Zea- 
land. Mount Maunganui. 
CARDITA CALYCULATA (kardium, the heart; caly- 
culus, a small bud).—A small, solidly-built bivalve of very 
asymmetrical shape, ornamented with twelve or more scaly 
ribs radiately arranged, very broad, and well marked in 
comparison to the size of the shell. In colour it is “white, 
yellowish pink, or dirty white” (Hutton). It is also known 
as the Mytilicardia, from having a beard like the mussels, 
and in general appearance bearing a superficial resemblance 
to the cockles. It attains a length of one and a quarter 
inches by three-quarters of an inch. Found below low- 
water mark to about fifty fathoms. 
Bay of Islands; Mount Maunganui; Island Bay; 
Chatham Islands. 
95 
Plate IX 
No. 13 
Sea Shells 
of New Zealand 
