Obituary: AN 261, 443 (1936); Weltall 37, 69 (1937)

Clemens discovered one IC object: the open cluster IC 4996 in Cygnus. He noticed it on a plate taken for the "Photographische Himmelskarte" with an 10.5" f/10.5 astrograph at Potsdam Observatory (June 13, 1896). He marked a cluster of 12 stars; see: Photographische Himmelskarte, Publ. Astrophys. Obs. Potsdam, Vol. 2, p. 221, plate 922. Dreyer incorrectly credits IC 4996 to Bellamy, who found the object in 1903.