In the plays of Plautus, there are some names ending in -um. They are generally formed as Greek names (whether genuine or pseudo-Greek), and the Latin ending -um here seems to correspond to the Greek ending -ον, as is usual.
Greek diminutives in -ιον, mainly names of women [...] appear in Latin with the ending -ium as well [as the ending -io]. Thus Φιλημάτιον takes in Latin the forms Philematium and (as here) Philematio.
When discussing Latin -ium names for women, Henry John Roby interestingly remarks that although these names belong to the feminine grammatical gender in Latin, they belong to the neuter grammatical gender in Greek. (Roby's specific examples are Planesium, Glycerium, Phronesium, Stephanium, Delphium.) (Grammar of the Latin Language from Plautus to Suetonius, Part 1, p. 106)
In Greek Personal Names and Linguistic Continuity, by Anna Morpurgo Davies, I found the following footnote:
13 Some women's names in Greek are neuter, but this need not count as an exception to the general need for marking sex differences. Men's names are never neuter. (p. 21)
Could anyone tell me more about the use of names ending in -ιον in Greek-language contexts? Did they trigger neuter agreement without exception, or might they show varying or mixed patterns of agreement (for instance, I wonder whether perhaps they could have triggered neuter agreement within the noun phrase—i.e. on the article and on attributive adjectives—but had natural gender agreement as a possibility outside of the noun phrase—e.g. on predicate adjectives)?