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As has already been said, I propose to make use of the structure of the 3% and 
4» pairs of the cirri for the classification of the species of the genus Badanus. I think that 
Fritz Mutrier was the first to observe that such claw-like spines occurred on the cirri of a 
species of the genus Balanus (B. armatus): according to him, they are in that species strongly 
developed on the segments of the 3", and on the posterior ramus of the 4‘ pair, but, in 
less developed condition, on some segments of the 5 and 6t cirrus also. On the same 
occasion he recorded the presence of such spines on the cirri of other species of Balanus, 
of which he gave B. improvisus, var. assimtlis as an example. Recently (1911), Kricrer 
pointed out a similar peculiarity in the cirrus of the 3" pair of B. ¢régonws Darwin, and in 
the mean time, the study of the species of Lalanus collected by the Siboga has shown that 
such armature is a common feature of several other species of this genus. In some species 
it is the 3" cirrus only which is armed, in others it is the fourth, and there are also species 
in which both cirri and sometimes the 2™¢ or the 52 also are furnished with these claw- 
like teeth. In other respects these species differ more or less considerably from one another, 
and so it has not been possible to include all of them in the same section of the genus 
Balanus. For, while some of these (4. amphitrite for an example) in every respect are 
true Balani, it cannot be denied that some of these species with armed cirri show resemblance 
to species of Acasta. Yet even the latter species, when we take all their characteristic features 
together, cannot be separated from 4a/anus. They must therefore remain in that genus but at 
the same time may be considered as forming the link between that genus and Acaséa. 
Besides the fact that it is not always the same cirrus (or cirri)*which shows (or show) 
the armature, another difference must be pointed out with regard to the shape of the 
teeth themselves. They are of two different types: on the cirrus or cirri of some species they 
appear like small triangular spines, which are attached to the surface of the segment with 
a rather broad basis and, as a rule, at some distance from each other. The surface of 
attachment can distinctly be made out as a small place of oval shape, exactly as is the case 
with other spines, or hairs, which, as a rule, have a rounded surface of attachment. The 
other type consists of teeth, which are like little hooks slightly curved downwards, or (seldom) 
upwards, and form so many chitinous excrescences along the margin, which often stands off 
like a list or rim on the surface of the segment. These teeth are close together, and form 
a saw-like structure. Transitions from teeth of the one type to the other are, however, not 
infrequent. 
I give here a list of the species of Ba/anus which I found furnished with armed cirri 
and which belong to the collection made by H. M.S. “Siboga” : 
Section Ortho-Balanus 
B. amphitrite: 3°4 cirrus, both rami with a row of downward-curving teeth along anterior face 
of numerous segments. One or more parallel rows of smaller teeth on the surface 
of the segments. 
4 cirrus, both rami have a group of smaller teeth on each of the 12 lower segments. 
B. alatus: 3" cirrus, the longer ramus with a few teeth between the hairs near the extremity 
33 
SIBOGA-EXPEDITIE XXXI14, 21 
