A new spatial ability test was administered online to 223 undergraduate students enrolled in introductory science courses. The 30-item multiple choice test measures individual differences in ability to identify the two-dimensional cross section of a three-dimensional geometric solid, a skill that has been identified as important in science, technology, engineering and mathematics (STEM) fields. Bivariate and partial correlations suggest that the test measures a skill that is distinct from three-dimensional mental rotation and change in view perspective. Test items varied along two scales: complexity of the geometric solid to be sliced and orientation of the cutting plane. Internal reliability of both the overall test and its subscales was satisfactory. Performance was higher on figures cut by orthogonal, rather than oblique, planes. Patterns of performance across more and less complex items, and patterns of sex differences on these items, suggest that items on the test are differentially amenable to imagistic and analytic strategies, with males outperforming females on items that are less amenable to analytic strategies. The test shows promise for online administration and for adaptation to younger populations. (Contains 5 figures and 3 tables.)