Notation of kind and numbers of fin-rays in bony fishes, used as character to tell apart genera and/or species. The hard rays or spines are noted in Roman numerals, the soft rays in Arabic numerals, the kind of fin by standard abbreviations Fins. E. g.: D XV-XVIII, 25-29. (If there are more than one D or A, the second or third portion usually does not have hard rays. Only the formulas of D and A are decisive characters for species and lower taxa, formulas of P, V and C, respectively, are only meaningful in genera, families or higher taxa. They are not referred to here. In Mormyridae the first three rays in D and A are unbranched, the first two rather small and easily overlooked. In the key offered here they are always included in the counts.