Web-based geometry transmission profits from a transmission system, which is both progressive and compressive. For this application, the wavelet transform has emerged as a suitable tool. We present a new zerotree coding scheme for compressing coefficients resulting from the wavelet transform of B-spline and Catmull-Clark surfaces. It results from a generalization of the original zerotree coding algorithm for image compression. The main idea is the construction of a suitable forest-structure of wavelet coefficients. Furthermore we present a system architecture for web-based progressive geometry transmission. Its main features are the separation of the transmission algorithms from the implementation of several geometry types, a set of parameters for regulating transmission properties, and a thread system for concurrent receiving and visualizing a scene. The power of the zerotree coding scheme is demonstrated by some numerical examples.