This is a catalog of galaxy clusters detected in a new ROSAT PSPC survey. The survey is optimized to sample, at high redshifts, the mass range corresponding to T > 5 keV clusters at z = 0. Technically, our survey is the extension of the 160 square degree survey (160d, the HEASARC Browse table called ROSGALCLUS). The authors use the same detection algorithm, thus preserving the high quality of the resulting sample; the main difference is a significant increase in sky coverage. The new survey covers 397 square degrees and is based on 1610 high Galactic latitude ROSAT PSPC pointings, virtually all of the pointed ROSAT data that were suitable for the detection of distant clusters. The search volume for X-ray luminous clusters within z < 1 exceeds that of the entire local universe (z < 0.1). The authors detected 287 extended X-ray sources with fluxes f_x > 1.4 x 10^-13 erg s^-1 cm^-2 in the 0.5 - 2 keV energy band, of which 266 (93%) are optically confirmed as galaxy clusters, groups or individual elliptical galaxies. The paper from which this table is extracted provides a description of the input data, the statistical calibration of the survey via Monte Carlo simulations, and the catalog of detected clusters. The authors also therein compare the basic results with those from previous, smaller area surveys and find good agreement for the logN - log S distribution and the local X-ray luminosity function. This sample clearly shows a decrease in the number density for the most luminous clusters at z > 0.3. The comparison of these ROSAT-derived fluxes with the accurate Chandra measurements for a subset of high-redshift clusters demonstrates the validity of the 400 square degree survey's statistical calibration. This Browse table contains the main cluster catalog (Table 4 of the reference paper) which comprises 242 serendipitously detected clusters of galaxies. It does not include 24 clusters within a redshift of 0.01 of the redshift of the target of the ROSAT observation (given in Table 5 of the reference paper), as these latter are not entirely serendipitous, 5 noncluster extended sources (given in Table 6 of the reference paper), nor 16 likely false X-ray detections (given in Table 7 of the reference paper). This table was created by the HEASARC in December 2007 based on the machine-readable version of Table 4 (the 'Cluster Catalog') obtained from the electronic ApJ website. This is a service provided by NASA HEASARC .