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26 I I I I I I I I I I I I I I I 'I I I I Demonstration Computer-interactive Keys for the Larvae and Early Juveniles of Selected Southwestern Catostomids (Hands-on Experimentation). Snyder, Darrel E. Larval Fish Laboratory. Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, CO Computer-interactive keys for the larvae and early juveniles of selected southwestern catostomids (suckers) are provided for hands-on experimentation. One covers the Catostomidae of the Upper Colorado River Basin (Catostomus ardens, C. catostomus, C. commersoni, C. discobolus, C. latipinnis, C. platyrhynchus, and Xyrauchen texanus). The other key covers most of the subfamily Catostominae of the Gila River Basin (c. Clarki, C. insignis, C. latipinnis, X texanus). Computer-interactive keys are more flexible and user-friendly tools for specimen identification than printed dichotomous or polychotomus keys. Among other features, users of such keys can limit consideration to only likely candidate species, have available characters listed in best (most diagnostic) order for remaining taxa, and select from that list in any desired sequence, bypassing characters that are unfamiliar, difficult to assess, or based on structures that are damaged or missing. Depending on the similarity of taxa included, such keys may be easier to prepare and are almost always much easier to correct, modify, or expand than more traditional printed keys. Most computer-interactive keys consist of a descriptive dataset and a commercial, share-ware, or free-ware program for its interrogation (see web site below for a list of such programs). The datasets for the keys presented were prepared in DELTA format (DEscriptive Language for Taxonomy-Dallwitz 1980; Dallwitz, et aI. 1993 onwards) and transformed for use by Intkey (Dallwitz et al. 1993 onwards, 1995 onwards), a widely used program available free over the internet (http://biodiversity. uno.edu/ delta/).