The design, construction, and measured results for a prototype module of probably the world's largest dense-packed, two-dimensional, ultrasonic (1.5-MHz) receive array is described. Containing over a quarter million diced elements, and a centrally located, constant beamwidth, spherical cap projector, the complete array was to consist of 25 modules, of which the central module is described. The individual receive element dimensions were (0.91x0.91x0.89) mm, with a center to center spacing of 1.07 mm. The ultrasonic spherical cap projector element had a 29-mm radius of curvature and an active angular aperture of 40 deg. Both projector and receive elements were designed to achieve a minimum 3-dB beamwidth of 30 deg at 1.5 MHz. In both cases the active material was piezoceramic. This presentation will discuss the various material tradeoffs associated with the selection of the: (1) active layer, (2) backing layer, (3) mechanical, and (4) electrical connections. Also the issues of dicing and back filling of the inter element interstices will be addressed. Measured acoustic calibration results for a small subset of receive elements and the projector will be presented.