In an attempt to determine the possible role of the pigment granule membrane in the mechanics of granule dislocation, the brown pigment-containing chromatosomes enveloping the ventral nerve chords of several palaemonid shrimps were examined by transmission electron microscopy in thin sections and freeze fracture replicas. In sections of component chromatophores, two distinct pigment granule types are discernible. The larger type, comprising membrane-bounded granules of about 460 nm diameter, contains a homogeneous, finely granular material and exhibits spherical to polymorphic profiles which show varying degrees of membrane scalloping; the other granule type, with granules some 60 nm in diameter, lacks a limiting membrane. In freeze fracture replicas, a single granule type, of about 430 nm diameter, exhibiting a sequence of from smooth to rough undulating membranes, is evident. A granule maturational process is proposed to be associated with this progressive scalloping of the limiting membrane. In the pigment granule membrane, intramembranous particles (8 nm in diameter) are scarce (approximately 90-200 particles/µm2) and apparently randomly distributed; no organized arrays are evident. Chromatophore plasmalemmas likewise contain few particles (approximately 200-400/µm2). These findings are discussed in relation to current models of pigment granule translocation. The pigment granule membrane is suggested to be an unimportant component of any movement mechanism, being assigned a diminutive role, if any, in linking the granule with its translocative force.