Mnaseas is reckoned to have been a pupil of a scholar who was chief librarian at what library?
Eratosthenes Eratosthenes of Cyrene ( ; Greek: Ἐρατοσθένης ὁ Κυρηναῖος , ] ;  – ) was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the terminology used today.
Scholarch A scholarch (Ancient Greek: σχολάρχης , "scholarchēs") was the head of a school in ancient Greece. The term is especially remembered for its use to mean the heads of schools of philosophy, such as the Platonic Academy in ancient Athens. Its first scholarch was Plato himself, the founder and proprietor. He held the position for forty years, appointing his nephew Speussipus as his successor; later scholarchs were elected by members of the Academy.