1976] Ashley, Tarter, & Watkins — Diploperla robusta 
311 
longitude and 38°22'52"N latitude. It varies in elevation from 
150.6 m at the mouth of Fourpole Creek to 355.1 m at a knob 
located in Salt Rock (Krebs and Teets, 1913). The tributary is 
3.2 km long and 1.5 m wide. The substrate of the stream bed is 
gravel and sand. The riparian woodland is primarily composed 
of box elder, Acer negundo L.; red maple, A. rubrutn L.; sugar 
maple, A. saccharum Marsh.; white oak, Quercus alba L.; red- 
bud, Cereis canadensis L.; and hop hornbeam, Ostrya virginiana 
(Mull.) K. Koch. 
Intensive and systematic field collections were made monthly 
between 26 April 1975 and 30 September 1976. The collections 
of naiads were done in ten minute sampling periods. A long 
handled dredge with a fine mesh net (60 threads per inch) was 
raked along the substrate. By kicking the substrate, the naiads 
were loosened from their habitat and drifted into the net, and 
subsequently were preserved in 10 percent formalin. 
Water temperature was measured with a mercury thermom- 
eter placed near the collecting site. The following water chemis- 
try parameters were measured with a Hach chemical kit. Model 
A1-36-WR: hydrogen ion concentration (pH), dissolved oxy- 
gen, total hardness, carbon dioxide, and alkalinity (carbonate 
and bicarbonate). 
In order to determine size classes, length-frequency histo- 
grams were arranged in 1 mm groups for 320 D. robusta naiads. 
The naiads were measured by a dial vernier caliper (nearest 0.1 
mm). The monthly index of growth was determined by head 
width which was measured for 320 D. robusta naiads by an ocu- 
lar micrometer (nearest 0.1 mm) in a Bausch and Lomb dissect- 
ing microscope. 
Naiadal food habits were determined by foregut analysis. For 
each month ten naiads were chosen at random. The foregut was 
removed by cutting off the head and making a ventral incision 
to the abdomen. The foregut was cut from the anterior end of 
the hindgut and placed on a slide with a drop of water. It was 
then carefully slit open and its contents emptied into the water. 
A Bausch and Lomb dissecting microscope was used to identify 
the contents. The percentage frequency of occurrence (%FO) 
was computed for each item and the average number of speci- 
mens with foreguts containing each item (x) was determined. 
To study the emergence pattern of D. robusta, the study area 
