hex.legend(col, at, labels=format(round(at)), legend.lab="Counts",
    height=3, lcex=1, width=1, inner, style="grayscale", minarea=0.04,
    maxarea=0.8, maxcount, density=-1)

col:

numeric vector of color numbers used to color the different levels in the color legend.

at:

numeric vector specifying the values at which the colors change.

labels:

a character vector of tick labels marking the value of at.

legend.lab:

a character string denoting a title for the legend itself. The default is "Counts".

height:

total height of the legend in inches. The default is 3 inches.

lcex:

numeric constant. Character expansion for the legend text. Default is 1.

width:

numeric constant giving the desired width of the legend. Default is 1.

inner:

numeric constant needed to determine the size of the hexagons. Default is computed as a function of width. (Inner diameter in inches.)

style:

character string. One of 5 possible styles for plotting the hexagons. This must be one of "grayscale","lattice","centroids","nested.lattice", or "nested.centroids".

minarea:

fraction of cell area for the lowest count. Default is 0.04 or 4%.

maxarea:

fraction of the cell area for the largest count. Default is 80%.

maxcount:

cells with more counts than maxcount are ignored.

density:

same as the corresponding argument in the function polygon. If density is zero, no shading will occur. If density is negative, the hexagons will be filled solidly.