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We study the distribution of X-ray selected clusters of galaxies with respect to superclusters determined by Abell clusters of galaxies and show that the distribution of X-ray clusters follows the supercluster-void network determined by Abell clusters. We find that in this network X-ray clusters are more strongly clustered than other clusters: the fraction of X-ray clusters is higher in rich superclusters, and the fraction of isolated X-ray clusters is lower than the fraction of isolated Abell clusters. There is no clear correlation between X-ray luminosity of clusters and their host supercluster richness. Poor, non-Abell X-ray clusters follow the supercluster-void network as well: these clusters are embedded in superclusters determined by rich clusters and populate filaments between them. We present a new catalog of superclusters of Abell clusters out to a redshift of z lim = 0.13, a catalog of X-ray clusters located in superclusters determined by Abell clusters, and a list of additional superclusters of X-ray clusters.

Abstract. We investigate the distribution of superclusters and voids using a new catalogue of superclusters of rich clusters of galaxies which extends up to a redshift of z = 0.12. The new catalogue contains 220 superclusters of rich clusters, of which 90 superclusters have been determined for the first time. Among them there are several very rich superclusters, containing at least eight member clusters.We demonstrate that two thirds of very rich superclusters are concentrated to a Dominant Supercluster Plane which is situated at a right angle with respect to the plane of the Local Supercluster and adjacent nearby superclusters.We apply several methods to estimate the characteristic distance between superclusters. The results indicate consistently the presence of a quite regular superclustervoid network with scale of ≈ 120 h −1 Mpc.Comparison with random supercluster catalogues shows significant differences between spatial distributions of real and random superclusters.We determine the selection function of the sample of clusters and suggest that the mean true space density of Abell clusters is 2.6 10 −5 h 3 Mpc −3 , twice the conventionally used value 1 .

According to the favour models for the formation of large-scale structure in the Universe (in which the dynamics of the Universe is dominated by cold dark matter), the distribution of galaxies and clusters of galaxies should be random on large scales. It therefore came as a surprise when a periodicity was reported 1 in the distribution of high-density regions of galaxies in the direction of Galactic poles, although the appearent lack of periodicity in other directions led to the initial report being regarded as a statistical anomaly 2 . A subsequent study 3−6 also claimed evidence for periodicity on the same scale, but the statistical significance of this result was uncertain due to small number of clusters used. Here, using a new compilation 7 of available data on galaxy clusters, we present evidence for a quasiregular three-dimensional network of rich superclusters and voids, with the regions of high density separated by ∼ 120 Mpc. If this reflects the distribution of all matter (luminous and dark), then there must exists some hithero unknown process that produces regular structure on large scales.During the past few years the number of clusters with measured redshifts has increased considerably. To search for the possible presence of a regularity of the distribution of matter in the Universe we have used a new compilation 7 of available data on rich clusters of galaxies catalogued by Abell and collaborators 8,9 . The compilation has made use of all (∼300) published references on redshifts of both individual galaxies and Abell galaxy clusters. Individual galaxies were associated with a given Abell cluster if they lay within a projected distance of ≤1.5 h −1 Mpc (1 Abell radius) and within a factor of two of the redshift estimated from the brightness of the cluster's 10-th brightest galaxy, using the photometric estimate of Peacock & West 10 (h is the Hubble constant in units of 100 km/s/Mpc). The compilation contains measured redshifts for 869 of the 1304 clusters with an estimated redshift up to z = 0.12. For the present analysis we used all rich clusters (richness class R ≥ 0) in this compilation with at least two galaxy redshifts measured. The omission of the 435 clusters without measured redshifts does not affect our result because an appropriate selection function was used.This cluster sample (including clusters with estimated redshifts) was used to construct a new catalogue of 220 superclusters of galaxies 11,12 . These are systems of clusters where the distances between nearest neighbours among member clusters do not exceed 1

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