Hi Betty Jean,
 
I don't want to wear out my welcome, but it's a slow day at the lab
and I'm fighting boredom!  Two hours to go!!  In general, the same
rules apply to subspecific names, whether geographic or not -
Oliva annulata amethystina
Cypraea caurica nigrocincta
Strombus gibberulus albus
Liguus fasciatus marmoratus
However, there are many names on the books that don't follow the
rules, especially older names.
Your mentioning of geographic forms brought to mind another aspect
that was not mentioned before.  There are certain specific suffixes
that are determined by the meaning of the specific name, rather than
by the gender of the genus name.  The most common of these are
specific names that either honor a person or indicate a geographic
locality.  For example, the ending "ensis" on a specific or
subspecific name indicates a geographic locality:
Conus bengalensis
Scutus sinensis
Nassarius capensis
Marginella thomensis
Fissurella barbadensis
Cypraea chinensis
Cardium guanacastensis
Cerithium erythraeensis
Bittium vancouverensis
Notice that the first three genus names above are masculine (ending
us), the next three are feminine (ending a), and the last three are
neuter (ending um).  However, the specific suffix (ensis) remains
constant.  It is not influenced by the gender of the noun.  "ensis"
translates "comes from", therefore:
chinensis means "comes from china"
vancouverensis means "comes from Vancouver"  (British Columbia)
capensis means comes from the Cape (in this case, of Good Hope)
and so on.  This suffix can also be used for subspecific names, as in
Conus floridanus floridensis.
The other common case where the adjective ending does not have to
match the noun ending is for species named after persons.  In this
case, the suffix of the specific name is determined by the gender of
the person whose name is used, rather than the gender of the noun
preceding.  The usual suffixes employed are "i"  for species named
after a male, and "ae" for species named after a female.
Cypraea walkeri
Trigonostoma withrowi
Euchelus lischkei
Conus boschi
Cerithium kochi
Sinum grayi
The above are all named after men, and have the masculine specific
suffix (i), even though 2 genera are feminine (a), 2 masculine (us),
and 2 neuter (um).
Teramachia dupreyae
Ancilla edithae
Conus memiae
Nassarius howardae
Cerithium judithae
Columbarium eastwoodae
The above are all named after women, and have the feminine specific
suffix (ae), even though 2 genera are feminine (a), 2 masculine (us),
and 2 neuter (um).
 
Regards,
Paul M.