Formation of a (2 x 1) local structure is found at submonolayer growth of Tl on the Si(1 1 1)-(7 x 7) surface by means of scanning tunneling microscopy (STM). At low coverages, the (7 x 7) grid remains and the (2 x 1) structure is formed inside of the half-unit cells of the (7 x 7). The (2 x 1) coexists with other structures, such as of "magic" clusters observed in the case of all other group III metals. Based on our STM observations we propose an atomic arrangement of the (2 x 1) structure. (C) 2008 Elsevier B. V. All rights reserved.