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We present Hubble Space Telescope (HST) WF/PC and WFPC2 observations of four rich clusters of galaxies at redshifts z ~ 0.4: CL 1447+2619, CL 0939+4713, CL 0024+1654, and Abell 370. Extensive ground-based observations have shown that all have substantial populations of blue, star-forming, and (in some cases) starbursting galaxies. We find the galaxy populations in these clusters to be approximately normal, in that most galaxies can be accommodated in the z = 0 Hubble sequence and have the luminosities, colors, and distributions within the clusters that are expected for their Hubble types. However, in every cluster environment the galaxy populations contain a uniformly higher proportion of late-type galaxies than is found in similar environments today.
Oemler et al. (Fri,) studied this question.