A cone-partitioned-plate fixture for the ARES rheometer (TA instruments, DE) has been designed, implemented, and validated. This geometry allows measuring the nonlinear shear flow properties of samples, which display edge fracture in regular cone-and-plate geometries, such as polymer melts and concentrated solutions. Reliable bulk shear flow data can be obtained with these systems at high rates and strains, using very small sample quantities. Measurements can be performed at temperatures ranging from at least -50 degrees C up to over 200 degrees C in a controlled nitrogen environment. An extensive set of start-up shear measurements on moderately entangled linear monodisperse polyisoprene (60 kg/mol) and polystyrene (182 kg/mol) melts to validate the design are presented and discussed with focus on the Cox-Merz rule and the characteristics of the stress overshoot. With this new geometry, the range of artifact-free data is extended by a decade in Weissenberg number (Wi(D)). It is shown that the obtained results compared well with the limited experimental data available from the literature on monodisperse polymer melts. Furthermore, we show that, for the investigated range of Wi(D) in start-up shear, the two monodisperse linear polymers of different chemistry with nearly the same number of entanglements, scale identically. (C) 2011 The Society of Rheology. [DOI: 10.1122/1.3625559]