The heat capacities of two members of a representative cubic mesogen, 4'-alkoxy-3'-nitrobiphenyl-4-carboxylic acid, were measured precisely. In accordance with the tendency reported previously for other members, the heat capacity in the cubic phase is smaller than that in the neighboring smectic C phase. The chain-length dependence of the reduction in the heat capacity upon the phase transition showed opposing trend depending on symmetry of the cubic phase ( Ia3d or Im3m). This finding is rationalized by assuming the existence of two aggregation modes ( rod and shell) in the Im3m phase in contrast to only the former mode in the Ia3d phase. (C) 2008 Elsevier B. V. All rights reserved.