According to the descriptions of P. dryinus as given by Persoon, and as followed by Fries and most later writers, the pileus is definitely lateral, and more or less Dimidiate, while in P. corticatus Fr.
"Studies of American Fungi. Mushrooms, Edible, Poisonous, etc."
George Francis Atkinson
34, 'Cicero in Limone hactenus laudat, "Tu quoque, qui solus lecto sermone, Terenti, conversum expressumque Latina voce Menandrum in medium nobis sedatis motibus effers, quiddam come loquens atque omnia dulcia miscens"; item C. Caesar, "Tu quoque, tu in summis, o Dimidiate Menander, poneris, et merito, puri sermonis amator.
"The Student's Companion to Latin Authors"
George Middleton Thomas R. Mills