Ryssadium

Ryssadium (Ῥυσσάδιον ὄρος, Ptol. 4.6.8), a mountain of Interior Libya, from which flows the Stacheir (Gambia), making near it the lake Clonia; the middle of the mountain (or lake?) 17° E. long., 11° N. lat. (Ptol. l.c.) This mountain terminated in the headland also called Ryssadium (Ῥυσσάδιον ἄκρον), the position of which is fixed by Ptolemy (4.6.6) at 8° 30′ E. long., and 11° 30′ N. lat. We assume, with Rennell and Leake, that Arsinarium is C. Verde, a conjecture which can be made with more confidence because it is found that Ptolemy's difference of longitude between Arsinarium and Carthage is very nearly correct,--according to that assumption this promontory must be looked for to the N. of the mouth of the Gambia. The mountain and lake must be assigned to that elevated region in which the Senegal and the Gambia take their rise, forming an appendage to the central highlands of Africa from which it projects northwards, like a vast promontory, into the Great Sáhara.

[E.B.J]