HEAD WIDTH, MILLIMETERS 
315 
1976] Ashley, Tarter, & Watkins — Diploperla robusta 
MONTH 
Figure 2. Monthly variation of the head widths in Diploperla robusta naiads 
from a small, woodland stream, Cabell County, West Virginia. Vertical lines 
= ranges, horizontal lines = means, dark rectangles = two times the standard 
error of the mean, larger open rectanges = one standard deviation, numbers = 
sample sizes, and solid lines = temperature (C). 
WATER TEMPERATURE 
