Traditional methods of observation applied to the sculpture of tectibranch shells and to the radulae of gastropods in general, have yielded a great deal of information regarding the structure of these organs, which are so important in taxonomy. In the genus Philine, for instance, the numerous European species can be reliably distinguished only by means of radular formula and shell-sculpture. In other genera the structure of these organs is also of crucial importance for identification. In most opisthobranch families the structure of the radular teeth is a uniquely reliable feature. Published descriptions of shell-sculpture in opisthobranchs have, however, not hitherto passed the handlens level of accuracy. The radula is customarily prepared for microscopic examination (following dissection, and cleaning in hot caustic soda or potash) by staining and mounting in balsam, or, more recently, in polyvinyl lactophenol (Thompson, 1958). These methods for the radula have the great disadvantage that it is necessary to squash the preparation considerably in order to examine the teeth. The results of squashing are somewhat unpredictable and, moreover, may distort or alter the natural relationships of the teeth, rendering difficult a functional interpretation of radular morphology.