Several modern genera and species have been

cyanobacteria of genus Hyella have several morphologi-cal characters that distinguish them from other cyano-bacterial genera. These characters include binary and multiple cell division; cells remain together surrounded by polysaccharide envelopes, forming pseudofilamentous, branched thalli, which penetrate calcium carbonate substrates. Cells differentiate in form and function in the course of development. Cell types can be identified based on their shape, function and location in the pseudofila-ment. Five types of cells, comprising apical cells, vegeta-tive cells, branch-point cells, baeocytes mother cells and baeocytes, could be identified. Very few species of euendolithic cyanobacteria have been reported to bore ooids in oolitic shoals (Lukas and Golubic, 1983; Al-Thukair and Golubic, 1991a). Oolitic shoals are usually found in tropical and subtropical marine environments world-wide, including the Bahamas