Hello Malia, A dichotomous key that would allow identification of any shell at random is simply not possible. If such a thing existed, it would be the size of the Encyclopedia Brittanica! The first thing you would need to identify a shell where the family is unknown would be a key to the families; then, once the family is identified, sub-keys within the family. But, even a key that could identify any unknown shell to family level would be impossibly complex. Shells actually are ideal specimens for teaching the use of dichotomous keys, and I used them years back when I was teaching zoology at the high school level. I had a box of about 80 shells, from various families, which I kept in the classroom permanently, and I had a dichotomous key which I wrote myself, which would allow positive identification of those 80 shells ONLY. Once you write a key that is accurate for 80 species, you quickly develop a sense of how complex such a key would have to be, in order to include several hundred species or more. My key to the 80 species was about 20 pages in length. The students found the exercise interesting, and some of them got pretty excited when they came up with the right name on their own. Alternatively, keys are available for some specific geographical areas, and for some specific groups of animals. For example, in one of my undergraduate invertebrate zoology classes we used a dichotomous key to the invertebrates of Cape Cod, which was published by the Woods Hole Oceanographic Institute. That key was a spiral-bound volume about an inch thick, and probably covered a thousand or more species. It began with a key to the phyla, then subkeys to the classes, orders, families, and species. It was pretty complex, even for college science majors, simply because many of the technical terms used were unfamiliar to anyone but the specialists who wrote the various keys. Paul M.