TARZAN

Tarzan of the Apes (McClurg - 1914)
The Return of Tarzan  (McClurg - 1915)
The Beasts of Tarzan  (McClurg - 1916)
The Son of Tarzan  (McClurg - 1917)
Tarzan and the Jewels of Opar  (McClurg - 1918)
Jungle Tales of Tarzan  (McClurg - 1919)
Tarzan the Untamed  (McClurg - 1920)
Tarzan the Terrible  (McClurg - 1921)
Tarzan and the Golden Lion  (McClurg - 1923)
Tarzan and the Ant Men  (McClurg - 1924)
The Tarzan Twins  (Volland - 1927) [Juvenile]
Tarzan, Lord of the Jungle  (McClurg - 1928)
Tarzan and the Lost Empire  (Metropolitan - 1929)
Tarzan at the Earth's Core (Metropolitan - 1930)
Tarzan the Invincible  (Burroughs - 1931)
Tarzan Triumphant  (Burroughs - 1932)
Tarzan and the City of Gold  (Burroughs - 1933)
Tarzan and the Lion Man  (Burroughs - 1934)
Tarzan and the Leopard Men  (Burroughs - 1935)
Tarzan and the Tarzan Twins w/ Jad-bal-Ja,
 the Golden Lion  (Whitman - 1936) [Juv.]
Tarzan's Quest  (Burroughs - 1936)
Tarzan and the Forbidden City  (Burroughs - 1938)
Tarzan the Magnificent  (Burroughs - 1939)
Tarzan and the 'Foreign Legion'  (Burroughs - 1947)
Tarzan and the Madman  (Canaveral Press - 1964)
Tarzan and the Castaways  (Canaveral Press - 1965)

BARSOOM (Mars) Series

A Princess of Mars  (McClurg - 1917)
The Gods of Mars  (McClurg - 1918)
The Warlord of Mars  (McClurg - 1919)
Thuvia, Maid of Mars  (McClurg - 1920)
The Chessmen of Mars  (McClurg - 1922)
The Mastermind of Mars  (McClurg - 1928)
A Fighting Man of Mars (Metropolitan - 1931)
Swords of Mars  (Burroughs - 1936)
Synthetic Men of Mars  (Burroughs - 1940)
Llana of Gathol  (Burroughs - 1948)
Tales of Three Planets  (Canaveral Press - 1964)
John Carter of Mars  (Canaveral Press - 1964)

PELLUCIDAR

At The Earth's Core  (McClurg - 1922)
Pellucidar  (McClurg - 1923)
Tanar of Pellucidar  (Metropolitan - 1929)
Back to the Stone Age (Burroughs - 1937)                                                                      Land of Terror  (Burroughs - 1944)
Savage Pellucidar  (Canaveral Press - 1963)

VENUS

Pirates of Venus  (Burroughs - 1934)
Lost on Venus  (Burroughs - 1935)
Carson of Venus  (Burroughs - 1939)
Escape on Venus  (Burroughs - 1946)
Tales of Three Planets  (Canaveral Press -1964)

CASPAK                                                                                                                 

     This qualifies as a series because in 1963 Ace Books issued the three parts of the story in separate volumes thus qualifying them as a series and becoming the first editions as thus.  As originally published it was a stand alone book.

The Land That Time Forgot  (McClurg - 1924)                                                                 The Land That Time Forgot (Ace - 1963)                                                                          The People Time Forgot (Cor Sva Jo) (Ace - 1963)                                                           Out of Time's Abyss (Ace - 1963)

NON SERIES

The Mucker  (McClurg - 1921)
The Girl From Hollywood  (Macauley  - 1923)
The Cave Girl  (McClurg - 1925)
The Bandit of Hell's Bend  (McClurg - 1925)
The Eternal Lover  (McClurg - 1925)
The Moon Maid  (McClurg - 1926)
The Mad King  (McClurg - 1926)
The Outlaw of Torn  (McClurg - 1927)
The War Chief  (McClurg - 1927)
The Monster Men  (McClurg 1929)
Jungle Girl  (Burroughs - 1932)
Apache Devil  (Burroughs - 1933)
The Oakdale Affair and the Rider  (Burroughs - 1937)
The Lad and the Lion  (Burroughs - 1938)
The Deputy Sheriff of Comanche County  (Burroughs - 1940)
Beyond Thirty and The Man Eater  (SF & Fant. Publications - 1957)
The Girl From Farris's  (Wilma Company - 1959)
The Efficiency Expert  (House of Greystoke - 1965)
I Am a Barbarian (Burroughs - 1967)