Drug delivery reservoir cassette for a pump is provided. The cassette includes a cassette housing having a front surface, a back surface and lateral sidewalls, the cassette housing defining a transverse axis extending between the lateral sidewalls and a longitudinal axis perpendicular to the transverse axis. The cassette housing includes a cassette body region defining a fluid reservoir chamber therein, and a cassette base region having a boundary configured to be received by the pump, the boundary including a pair of opposing rails disposed on opposite sides of the longitudinal axis. The cassette base region can also include an engagement surface, alignment key, and/or support rib to align the cassette in a receiving region of the pump. A device for delivering a beneficial agent including a pump and cassette is also provided.