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I briefly reviewed the formation, evolution and properties of boxy/peanut bulges and of disc-like bulges. These two types of objects have very different formation and evolutionary histories and very different properties. B/Ps form from vertical instabilities and their building blocks are the 3D families associated with the 3D bifurcations of the x1 family. Discy bulges form from the inflow of (mainly) gas material and from the ensuing enhanced star formation. Thus B/Ps are mainly constituted of inner disc stars, while the discy bulges have a very large contribution from gas and young stars. Since the formation of discy bulges relies on the gas inflow, it is expected that they will be found mainly in late type disc galaxies, as is indeed the case. The face-on extent of the B/Ps is of the order of five times larger than that of the discy bulges and, seen edge-on, they extend well outside the equatorial plane, while the discy bulges are thin. Their kinematics and their contribution to the radial photometric profiles are different from those of discy bulges. Thus, one should clearly distinguish between B/Ps and discy-bulges and not lump together them in a single category.

Once this has become clear, one may also wish to revise the existent nomenclature in order to avoid some of the present confusion. Boxy/peanut bulges could be called boxy/peanut features (or structures), or simply peanuts, as proposed in A05. This would make it clearer that they are just a part or a feature of the bar and not an independent entity. Similarly, discy bulges could be simply called inner discs. Then the name `bulge' would be reserved for classical bulges. This change, however, will also necessitate changing the bulge definitions described in Sect. 1.


I thank my collaborators, A. Bosma, A. Aguerri, C. Heller, I. Martinez-Valpuesta and I. Shlosman, for interesting and fruitful discussions. This work was partially supported by grant ANR-06-BLAN-0172 and by the Grüber foundation.

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