The surface of the vilayet is generally mountainous, except in the central valley of the Maritza, and along the banks of its tributaries, the Tunja, Arda, Ergene, &c. On the west, the great Rhodope range and its outlying ridges extend as far as the Maritza, and attain an altitude of more than 7000 f t.
The interesting little Rhodope veranyii, which has no odontophore, has been associated by systematists both with these simplified Opisthobranchs and with Rhabdocoel Planarians.
(1883); Bohmig, " Zur feineren Anatomic von Rhodope veranyi, Kolliker," Zeitschr.
The most distinguishing features of the country were the chain of Rhodope (Despoto-dagh) and the river Hebrus (Maritza).
The greater part of the country is hilly and irregular, though there are considerable plains; but besides Rhodope two other tolerably definite chains intersect it, one of which descends from Haemus to Adrianople, while the other follows the coast of the Euxine at no great distance inland.