Hellenica Oxyrhynchia is the name given to a history of late 5th and early 4th centuries BC in ancient Greece, of which papyrus fragments were unearthed at Oxyrhynchus, in Egypt. One of the two major fragments, the so-called "London papyrus," found in 1906, deals with battles in the late Peloponnesian War, particularly the Battle of Notium. The other, the "Florentine papyrus," found in 1942, deals with events in the early 4th century. The entire history seems to have been a continuation of Thucydides covering events from 411 BC to 394 BC.
The discovery of the first papyrus in 1906 led to a shift in the degree of credence which historians assigned to the ancient sources of the period. In the 19th century, Xenophon, a contemporary of the events he described, was presumed to be universally preferable to the much later Diodorus Siculus. The Oxyrhynchus historian (named "P." for "papyrus"), however, whose work won praise for its pragmatism and style, was found to gibe better with Diodorus's account than with Xenophon's on several key issues. This led to a reevaluation of the values of these sources, and modern historians now prefer Diodorus' account at a number of points.
Modern scholars have debated extensively over P's identity. Among the historians suggested have been such prominent names as Ephorus and Theopompus, but most of these have been strongly objected to on grounds of style, presentation, or subject matter. At present the most likely candidate seems to be Cratippus, an Athenian historian of the 4th century. The style, biases, and coverage (Cratippus's work is known to have been a continuation of Thucydides) support the identification, although issues have been raised.
Fine, John V.A. The Ancient Greeks: A critical history (Harvard University Press, 1983) ISBN 0674033140
Hornblower, Simon, and Anthony Spawforth ed., The Oxford Classical Dictionary (Oxford University Press, 2003) ISBN 019866172X