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British Museum, Darwin continued, and this without the operculum, as just stated, and, of course, 
without the animal’s body. 
Since this was written, the species was mentioned in two papers: in BorrapaILe’s Marine 
Crustaceans of the Maldive and Laccadive Archipelagoes (1903), and in ANNANDALE’s Cirripedia, 
in the “Ceylon Pearl Oyster Report” (1906). BorrapaiLe, however, was unable to find in his 
specimens the rows of holes between the ridges of the basis as described by Darwin and, 
therefore, thinks it possible that his species is different from Darwin’s. He gave a short 
description of the opercular valves of his species. ANNANDALE says about the species he has 
investigated that it agrees closely with Borrapate’s description as regards the structure of the 
operculum; as for the apertures of the basis, which BorrapaILe was unable to see, ANNANDALE 
reports that they are absent in some samples he has examined. “In one individual, however, 
there appear to be indications that they have been present, but have been almost obliterated 
during growth”’. 
Of course, it is possible that something of the kind has happened in the case of the 
specimens from the Gulf of Manaar — all I can say is, that the Siboga dredged several 
specimens of alanus which no doubt belong to Darwin's species, and the basis of which 
distinctly shows the remarkable structure mentioned by that author. The description of the 
opercular valves given by Borrapattr, although agreeing in several respects with that of the Siboga 
specimens, is too short to be absolutely decisive. Yet, what BorrapaILe says about the tergum: 
“Apical tooth present, but broken in the specimen” seems to prove that his determination is right. 
The Siboga-specimens have the shell (Pl. XX, fig. 17) white and strongly ribbed longi- 
tudinally; the ribs near the basis are produced into points or spikes, which correspond with 
such spikes at the circumference of the basis. The length of these spikes in the Siboga- 
specimens is, perhaps, not quite so great at it was in the specimen studied by Darwin. The 
shape of the shell is conical, somewhat elongate in its rostro-carinal axis. The orifice is 
small, pentagonal, toothed. The radii are narrow and have oblique summits. The carino-lateral 
compartments are narrow. 
The basis is distinctly concave and has the circumference produced into spikes as 
already mentioned. The internal surface has slightly prominent ribs radiating from the centre 
to the surface, and between these, rows of small openings are seen. These apertures are 
of somewhat irregular shape and unequal sizes; they are mostly placed in a single row, here 
and there, however, in an irregular double row. The shell is almost entirely covered by a 
thick yellowish coat which seems to be a sponge; the ribbed structure appears distinctly only 
after this has been taken away. The size of the shells in the larger specimens is: 3'/, mm. 
greatest diaméter of the basis, and a height of 2'/, mm. 
~The scutum (Pl. XX, fig. 18, @ and c) has prominent growth-ridges, terminating at 
the occludent margin in very prominent teeth. In larger specimens the upper part of the outer 
surface does not show these ridges so distinctly, nor are the teeth of the occludent margin 
so prominent here. At the inner side, the articular ridge is long but not very prominent; the 
adductor ridge is well-developed. At the basi-tergal corner there is a well-marked cavity for 
the lateral depressor muscle. 
80 
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