In The Importance of Being Earnest, who is Egeria, and why might Chasuble refer to Miss Prism in this manner?

Act II of 's
shows the flirtatious relationship between the reverend Dr. Chasuble and
the prude Miss Prism as they meet during one of Chasuble's presumably usual visits to the
Worthing country estate.

At the time that the reverend enters the home, Miss
Prism is with Cecily performing her duties of governess. After a brief dialogue, Chasuble,
referring to Laetitia Prism says

But I must not disturb
Egeria and her pupil any longer.

He does this as a flirty
way to play on the similarities between the name "Laetitia" and  the name
"Egeria". There are two different postures as far as the use of Egeria goes.

Similarly to the historically-known pagan character of the mythical
"Laetitia" (Prism's first name), "Egeria" is likewise a Roman
goddess.

Egeria is said to have been nymph of water and springs, and an
adviser, as well as lover, to the second King of Rome, according to the pagan legend. This would
have been quite a saucy, yet,  subtle mischievous remark from Chasuble to Prism, who is the
epitome of the prudent and prudish woman.

Also the name of Egeria belongs to
a female writer from the (pagan) Roman times who is thought, thus far, to be the first
ever-published woman in the history of the world. As we know, Miss Prism proudly calls herself a
female writer, and also claims to have completed a novel.

Hence, the
connection is two-fold between the two names. "Egeria" and "Laetitia" are
both Roman goddesses. The connection of the name "Egeria" with the character of Miss
Prism is also that Egeria is a pilgrim writer whose writings have made history, while Miss Prism
also boasts of having written a novel, whose manuscript she claims to have "lost" or
"misplaced".

It is this precisely the loss of this
manuscript that incites the action in the play, for this misplacement results in the leaving of
baby Jack Worthing inside of a handbag at the cloakroom of Victoria Station...the Brighton Line.