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mostly because subdivided characters incurred more character-dependency problems (avail- ability of certain characters depending on the character state selected for a controlling char- acter-e.g., if yolk is not present, yolk-related characters should be made unavailable). Although lntkey can make extensive use of taxon and character-state-selection images, preparation and inclusion of such were neither critical for operation of the key nor logistically and budgetarily feasible for this expanded update of the guide (if there is enough interest and support, they could be prepared and incor- porated at some future date). Also, such images can require a considerable amount of storage memory and at times a strictly text key may be preferable, especially for the experienced user or when using a slower computer with limited memory. Instead, the printed illustrations herein are referenced extensively and should be avail- able when using the key. However, as examples of how character-state-selection images func- tion, such illustrations were prepared and included in the key for developmental phase, SL, and phases of gut development. Interim and near final versions of the key were subjected to in-house testing, mostly in the routine processing of UCRB collections, and refined accordingly. Based on reviews and user feedback, future refinements of the key will likely be implemented and made available over the Internet. Clearing and Staining Procedures for Skeletal Study of Small Fish These instructions are modified from Snyder and Muth (1988) and based on proce- dures detailed by Fish (1932, Method III), Taylor (1967), Potthoff (1984), and Taylor and Van Dyke (1985). See Taylor (1967) and Taylor and Van Dyke (1985) for detailed explanations and discussions of the various steps, factors affecting them, and alternatives. The procedures that follow are for differ- ential staining of cartilage and bone beginning with living specimens. If using previously preserved specimens, staining only for cartilage, staining only for bone, or clearing (making transparent) without staining, skip the irrelevant steps. Minimum and maximum times given in the procedures are approximate for single specimens measuring 10 and 25 mm TL, respectively, and processed in 20 mI vials. Times for other sizes and numbers of specimens can be approximated accordingly. Vertebrates as large as 500 mm have been cleared and stained by these proced- ures but time requirements are considerably greater; clearing alone can take several weeks. Potthoff (1984) provides a diagram of approxi- mate times for specimens 10 to 500 mm SL. Specimens larger than 30 mm with scales or thick skin may need to be scaled or skinned, or selectively and carefully punctured over the body with a sharp needle, prior to clearing and staining. Some larger specimens may need to be eviscerated. Fatty or oily specimens may need "degreasing" in xylene before staining or clear- ing and specimens with large amounts of guanine or similar white or silvery substances may need soaking in 2% or stronger potassium hydroxide solution after clearing by the enzyme method (Taylor and Van Dyke 1985). Specimens should never occupy more than 25% of solution volume during fixation; lesser percentages (e.g., 10%) are recommended. Dur- ing clearing and staining, results will be better and time requirements may be less if specimens occupy much less than 10% of solution volumes (e.g., down to 2% of solution volume during neutralization and clearing). For specimens 30 mm TL or less, most or all steps can be carried out conveniently in 20 ml or similar-size vials. During each step, periodically turn or move specimens to minimize solution stratification and aid penetration of solutions into tissues of specimens being processed. For the most reliable results begin with freshly fixed and preserved specimens. Older museum specimens mayor may not clear and stain properly depending on original fixative, preservative, and subsequent care. However, properly fixed and preserved specimens should clear and stain nearly as well as fresh material, even after a few decades. With specific regard to fish embryos and larvae, Taylor and Van Dyke (1985) made the following observations. "The presence of carti- lage in embryos and larval fishes is readily determined by this method [differential staining with enzyme clearing]. But, determining the 22