using mtext with lattice plots and grid.arrange

I am trying to add an A and B labels to two lattice plots I have combined using the grid.arrange function. I cannot get the B label to show up where I would like it to. I would like the letter A to be to the left and above the top plot and the letter B to be left and above the bottom plot. I have tried changing the line code to different numbers with no success.

Here is some example data:

  data1<-data.frame(x=c(1:60),y=rep(c("A","B"),each=30),w=rep(c("V1","V2","V3"),times=20))

Plotting Code
require(lattice);require(grid.Extra)

p1<-bwplot(x~y, data = data1, groups = w, 
       pch = "|", box.width = 1/6,  par.settings =mytheme ,scales=list(x=list(cex=1.2),y=list(cex=1.2)),
       ylab=list("Number of Scallops per Station",fontsize=15),xlab=list("Strata",fontsize=15),
       panel = panel.superpose,
       panel.groups = function(x, y, ..., cex,group.number,col) { 
           panel.bwplot(x + (group.number-1.5)/6,y,...) 
       }) 

p2<-barchart(x~y|w,type="count",layout=c(3,1),data=data1,
    col="light gray", xlab="Binned Number of Scallops per Station",ylab="Count",horizontal=F,
    strip = strip.custom(bg="white",strip.levels = T),as.table=T,origin=0,family="A",
    scales=list(relation="same",alternating=1,x=list(cex=1.2),y=list(cex=1.2)),
    par.settings = list( grid.pars = 
    list(fontfamily = 'serif',cex=1.2)),
    panel=function(x,y,...){
    panel.barchart(x,y,...)})

grid.arrange(p1,p2)

mtext("A",3,line=2,cex=1.2,at=0,family="serif")


 #not in the correct area

mtext("B",3,line=25,cex=1.2,at=0,family="serif")


sessionInfo()
R version 3.3.1 (2016-06-21)
Platform: i386-w64-mingw32/i386 (32-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

Solution

mtext() is for base graphics, the grid equivalent is grid.text,

library(lattice)
library(gridExtra)
library(grid)

p1 <- p2 <- xyplot(1~1)

grid.arrange(p1, p2)
grid.text(c("A","B"), x=0, y=c(0.5, 1), vjust=1, hjust=0, gp=gpar(fontface=4))