sh-alias-alist

sh-alias-alist is a variable defined in `sh-script.el'.
Its value is

((csh . tcsh)
 (ksh . pdksh)
 (ksh . ksh88)
 (bash2 . bash)
 (sh5 . sh)
 ("^/system/bin/sh$" . mksh))

Documentation:
Alist for transforming shell names to what they really are.
Use this where the name of the executable doesn't correspond to
the type of shell it really is. Keys are regular expressions
matched against the full path of the interpreter. (For backward
compatibility, keys may also be symbols, which are matched
against the interpreter's basename. The values are symbols
naming the shell.

You can customize this variable.