、。
She invited two classmates — Jane and Mary, that is.
Literal
She [topic-は] classmates two-people, [namely-つまり] Jane [and-と] Mary [object-を] invited.
An apposition: '級友二人' is named first as a description, then つまり ('namely, in other words') introduces the names that fill that description. This rhetorical move — describe-then-name — is common in Japanese exposition and reads as deliberate, slightly formal. 級友 itself is a faintly literary word for classmate, less colloquial than クラスメート (the English-derived loan) or 同級生 (the everyday compound). The と here is the listing と, exhaustively pairing the two names. The counter 二人 is the standard counter for people, with the irregular reading ふたり.