The merry Greek, tart Aristophanes, Neat Terence, witty Plautus, now not please ; But antiquated and deserted lie, As they were not of Nature's family.
This passage mentions classical comedians whose works are no longer pleasing to Nature now that she has read Shakespeare.
The description of them as "antiquated and deserted" is pretty ironic, since they are definitely antiquated, having been born centuries before, and they were, in Jonson's time, for the most part deserted. The classical works were just beginning to come back into popularity when Jonson died, but he was definitely one of the few who had the mind or money to devote to reading those authors during his lifetime.
The reference in line 54 to "Nature's family" is interesting and plays into our nature vs. art debate, discussed earlier. Stating that these ancients were not of Nature's family implies that Shakespeare is. This is significant because it ties back into the idea that Nature produced Shakespeare and that his gifts are naturally endowed, as opposed to earned or developed.
Yet must I not give Nature all ; thy art, My gentle Shakspeare, must enjoy a part. For though the poet's matter nature be, His art doth give the fashion : and, that he
Oh wait, but here's a caveat. According to lines 55 and 56, Jonson thinks Shakespeare's "art" deserves some recognition, too.
Art, in the 1600s, had a more complicated meaning than we think of it as having today. Here, the word "art" is referring to craft, not in the third grade papier-mâché way, but in the trade, skill, job sense of the word.
By saying Shakespeare's "art" is worthy of praise, Jonson is acknowledging that Shakespeare did have to put in some effort into producing and perfecting his plays. It wasn't all nature-given talent.
Lines 57-58 sum up Jonson's viewpoint nicely: a person could naturally be a poet, but craft and skill are required to "fashion" that gift into the enduring literature Shakespeare has created.