Samples from Hole 1138A were prepared for diatom analysis (see Bohaty et al., this volume) using standard procedures for light microscopy. Two preparations were made for each sample: an unprocessed or "raw" preparation and a processed preparation. Two subsamples (~0.25 g) for each interval were placed in 15-mL centrifuge tubes. One set of subsamples was left to soak in deionized water, and the other was chemically treated. The treated samples were initially reacted with ~5 mL of 10% hydrochloric acid in order to remove the carbonate component (i.e., nannofossils, foraminifers, and diagenetic cements). The centrifuge tubes were then shaken on a vortex stirrer and left to react for 1 hr. Following these steps, ~5 mL of 30% hydrogen peroxide was added to remove organic material and help disaggreagate biosiliceous "clumps." The samples were soaked overnight in the HCl/H2O2 solution and then thoroughly washed by centrifuging three times at ~1500 rpm for 10 min. The chemically treated samples were not heated during preparation.
Strewn slides of all samples were made on 20-mm x 40-mm coverslips. Each centrifuge tube was filled with ~8 mL of deionized water and then mixed on a vortex stirrer. After settling for 30 s (in order to settle the sand-sized fraction), a small aliquot was removed from the center of the suspension with a pipette. Two or three drops of sample were then dropped on a coverslip containing a thin film of deionized water. All samples were mounted in Norland optical adhesive 61 (refractive index = 1.56).
Slides were examined at 250x, and specimens were counted until a total of 300 specimens were reached. Where a count of 300 specimens was reached before the entire slide was examined, the portion of the slide analyzed is listed in the tables to give an understanding of the relative abundance of silicoflagellates. When specimens were rare, the survey was ended before finishing the slide, with the amount of slide examined listed in the abundance tables. Only those fragments representing more than one-half of a silicoflagellate were included in the counts. Because the number of teratoid (aberrant) specimens may be an indication of environmental stress, a separate tally was made of these. Aberrants include specimens with fused spines or struts, two struts attaching to a basal side, or distorted basal rings (see McCartney and Loper, 1989, for a discussion on the basic rules of silicoflagellate form). Because the aberrants are often counted among the specific taxa, the number of aberrants is not included in the total counts.
The Hole 1140A portion of this study was conducted by undergraduate students having limited experience with silicoflagellates. Although the work was closely supervised by the first author, the relative inexperience of these students should be taken into account when evaluating the results. For Hole 1140A, Robb Engel did the microscopic work for Cores 183-1140A-1R through 7R, Rita Williamson conducted the census for Cores 183-1140A-8R through 13R, and Tracy Reed obtained the data for Cores 183-1140A-14R through 22R. These students had frequent discussions among themselves and with their teacher (Kevin McCartney) in order to obtain as consistent a species concept as was reasonably possible.