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long and careful consideration I came to the conclusion that die safest way was to consider 

 them as belonging to two different varieties only : the one already described by Darwin as 

 var. (i) communis, the other different from those proposed by Darwin, and now named 

 var. (10) malayensis, 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, II Ir and 

 VIII (probably). 



B. amphitrite, var. malayensis n. var. : the samples II, \\\a, \\\b, IV, V, VI and VII. 



The two varieties may be distinguished by the following characters : 



Var. (i) 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 rosé 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 (PI. 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 (PI. 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. 



Pal pi (PI. XIV, fig. 12*) elongately oval, with the upper margin straight, or even 

 slightly hollowed out, and the basal margin rounded. The spines on the 011 ter surface are 



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