The genome of the Atlantic sheepshead minnow, <u>Cyprinodon variecratus</u> (cyprinodontidae) contains at least two highly repetitive satellite DNA sequences. The major satellite sequence is present at roughly 10⁶ copies per haploid genome. The basic repeating unit averages 170 bp in length, tandemly arranged, and is bracketed by a Hind III restriction site. The Hind III satellite has little or no sequence similarity with other fish satellite DNAs reported in the 1iterature. Comparative hybridization experiments detect related sequences in the genomes of several species of pupfish of the genus <u>Cyprinodon</u> as well as in some cyprinodontid species of the genera <u>Jordanella</u> and <u>Floridichthys</u>. No significant hybridization was detected with the New World species <u>Cualac tesselatus</u> and Megupsilon aporus or within species of the Old World genera <u>Valencia</u> and <u>Aphanius</u>. / Ph. D.