Scatter plots do not allow any of the markers to be hidden. A Scatter plot will display a marker for every point you are plotting. If you want to hide the markers for one of your variables, you need to create a Line plot. This plot gives you complete control over the number of markers displayed and the line between the points.
KaleidaGraph is a thoughtfully designed graphing and data analysis application for research scientists, as well as for those in business and engineering fields. It produces publication-quality graphs, and easily converts the most complex data into a functional display.