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KOHMAN Y . ARAKAWA
type of the pellets was the sculptured rod from which may be evolved
more complex forms, e.g. unsculptured rods, ribbons and ovoids.
Sculptured rod-types faeces prevail in the phylogenetically lower bivalves, such as the Protobranchia, whereas in the higher ones, such as
the Eulamellibranchia, the rod and ovoid pellets predominate.
Thiele (1935)
50 Order TAXODONTA
I I
n
n
Pel let-types
Fig. 23. Frequency distribution of types of pellets produced by the bivalve orders
Taxodonta, Anisomyaria and Eulamellibranchia (Thiele, 1935).
To facilitate comparison the distribution of the various types of
bivalve faeces in relation to different schemes of classification proposed
by various authorities has been set out in tabular and histogrammatic
forms (Table V ; Figs. 21 to 25). Of these schemes, that of Purchon
(1963) appears as the best when considered in relation to the distributions of pellet-types, because the grouping of these agrees more
closely with his classification than with those proposed by Dall (1894),
Pelseneer (1911), Thiele (1935) and Cox (1960).