[Invited] Review paper delivered at the Fifth OAC Workshop on the Morphological and Physical Classification of Galaxies; Sant'Agata sui due golfi 3-6 Sep 1990, to be published by Kluwer Press.

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Abstract. A review of the structural properties of BCM's in poor and rich clusters is presented in order to define the morphological types gE, D and cD in ellipticals. Although the difference between bright field ellipticals and BCM's is subtle (primarily an enlargement in characteristic radius for BCM's) it is quantifiable on the fundamental plane for ellipticals. Various indirect arguments, plus direct comparison to N-body simulations, demonstrate that these structural differences are the result of a past history of early mergers plus late accretions of lesser clusters members. Although present day tidal stripping is evident in some clusters, cD envelopes must have their origin before cluster virialization.

Table of Contents

• INTRODUCTION
• BCM MORPHOLOGICAL TYPES
• CLASSIFICATION BY SURFACE PHOTOMETRY
• ARE BCM'S AN EXTENSION OF THE NORMAL ELLIPTICAL SEQUENCE?
• ARE cD ENVELOPES PRIMORDIAL IN ORIGIN?
• SUMMARY
• REFERENCES
• DISCUSSION