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long and careful consideration I came to the conclusion that the safest way was to consider 
them as belonging to two different varieties only: the one already described by Darwin as 
var. (1) communis, the other different from those proposed by Darwin, and now named 
var. (10) madlayensis, from being, apparently, rather common in the Malay Archipelago. In 
some respects several of the samples approach to some of the other varieties, as described by 
Darwin, but the resemblance was in no case complete, or so striking, as it was in that 
of sample IX, with Darwin’s figure and description of B. amphitrite var. communis. The 
samples can be best divided into the two varieties in the following way: 
B. amphitrite, var. communis Darwin: the samples IX (certainly) and I, IIc and 
VIII (probably). 
B. amphitrite, var. malayensts n. var.: the samples II, IIIa, IIIé, 1V, V, VI and VII. 
The two varieties may be distinguished by the following characters: 
Var. (1) communis: shape of the shell conical, with small orifice, or, where the speci- 
mens are crowded, cylindrical, with larger orifice. Radii narrow, with very oblique 
summits. Colour white, with regular longitudinal stripes of violet. or blue-grey 
colour, crossed by horizontal lines of greyish-white. Scutum with a very prominent 
adductor ridge and the articular ridge also prominent and half as long as tergal 
margin only. 
Var. (10) malayensis: shape of the shell cylindrical or flattened laterally, with large 
orifice. Radii broad at upper extremity, with somewhat oblique, often concave. sum- 
mits. Colour very variable, from almost white or light rose to dark red and purple; 
longitudinal stripes of darker colour, freckled with white or red in irregular horizontal 
rows. Radii often dark red or purple. Adductor ridge of the scutum not very pro- 
minent, and the articular ridge more than half as long as the tergal margin (Pl. XIV, 
fig. 8—17). 
I investigated the structure of the body of numerous specimens of different stations. In 
many respects the specimens of different varieties show the same type, in other points, how- 
ever, differences of some importance were observed. As might be expected, even specimens of 
the same locality often show small differences, and these are, of course, more striking when - 
specimens from different stations, although belonging to the same variety, are compared. Not to 
be too extensive, I will give a general description of the different parts and I will add, for 
the two varieties, only the principal differences I observed. 
Mouth. Labrum (Pl. XIV, fig. 12) with the notch deep, but not very wide at the 
entrance. The lateral parts are rather broad, with the angles rounded. The normal number of 
teeth is 4 on each side. They are, as a rule, rather strong and pointed, the innermost one 
is situated at, or in the entrance of the notch, the others all very close together. The 
sub-triangular, shield-like thickening, is broad, its vertical dimension considerably shorter than 
the breadth. 
Palpi (Pl. XIV, fig. 12%) elongately oval, with the upper margin straight, or even 
slightly hollowed out, and the basal margin rounded. The spines on the outer surface are 
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