There died a myriad, And of the best, among them, For an old b**** gone in the teeth, For a botched civilization,
In lines 86-87, Pound's still talking about the "myriad" (which means "whole bunch of") men who died in WWI, and says that some of the "best" men of the time were among them. And what did they all die for? For what Pound calls a "botched civilization," an ugly modern world that isn't worth fighting for. And in case he hasn't made his point about how terrible the modern world is, Pound compares modern civilization to "an old b**** gone in the teeth."
Charm, smiling at the good mouth, Quick eyes gone under earth's lid,
For two gross of broken statues, For a few thousand battered books.
Pound's been giving the modern world quite a pounding, so why would he say in line 90 that the world has "charm" and a "good mouth?" Well the main reason is because Pound is being really sarcastic here, since the world is not a charming place and its mouth isn't good because it just tells lies to people.
The "Quick eyes gone under the earth's lid" likely refers to the eyes of the soldiers, which would've had to be quick to see the enemy firing in WWI. These eyes, though, have gone under the earth's lid because these people have died and have been buried under the earth's surface.
And for what did all of these good people die? Well according to Pound, they died for "two gross [twelve dozen, or 144] of broken statues" and for "a few thousand tattered books." Here, Pound uses the metaphors of the broken statues and tattered books to say that the soldiers were fighting for a civilization that was already ruined.
And believe us, World War I was totally sold on the idea of defending culture. Just check out this poster. Pound, though, is saying that going to war to defend culture was a totally empty gesture, since culture was already broken.