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What is the relatum
of the shape of the
shell to the principies
mentioned above?
drawn out into very long spine-like processes situated in the same direction as the longitudinal
axis of the body; see the accompanying fig. XVII.
In some species, e. g. Conchoecia imbricata (G. S. Brady) and C. symmetrica
G. W. Müller (see fig. 1 of the latter species in the special part of this work) the rostrum
is well developed and the posterior dorsal corner of both the right and the left valve is
Fig. XVII. — The shell of Conchoecia caudata G. W. Müller. seen from the side. (From G. W. Müller, 1906a.)
furnished with a spine-like process situated in the same direction as the longitudinal axis
of the body but considerably shorter than in C. caudata; in addition some of these species
have weak processes, pointing about in the same direction as the first-mentioned processes
and corresponding to the mucrones in a number of Cladmera. The characteristic feature of
all the processes so far mentioned is consequently that they point in the same direction as
the longitudinal axis of the body. In otliers the shoulder ridges on the shell are differentiated
as more or less powerful wing-like processes; these are found, for instance, in Conchoecia
alata G. V . Müller and Halocypris cornuta G. W. Müller (see G. W. Müller, 1906a, pi. XXIX,
figs. 1 and 2 and pi. VIII, figs. 1 and 3),
Only in one species (Thaumatocypris echinata G. W. Müller) do we find on the shell
a number of spines pointing in different directions; see the accompanying fig. XVIII.
What view are we to take of these
processes and spines?
The only writer who has touched on this
question is A. STEUER. In this author’s work
of 1910 they are denoted (p. 208) as buoyancy
organs. It will soon, however, be obvious to
anyone who studies these matters in detail
that this explanation cannot be an adéquate
one. If we look, for instance, at the posterior
part of the shell in Conchoecia daphnoides, we
shall see that this is rather decidedlv flattened
at the sides, i. e. its horizontal section is rather
slight. That the two pairs of spines in the
genus Thaumatocypris cannot be expia ined as
adaptations of buoyancy is shown quite clearly
by their position, as they are not, as one would
expect according to the buoyancy theory, botli
(From G. W. Müller, 1906a.)
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