To answer the specific question, yes, it is correct to change Mitra tuberosum to Mitra tuberosa. The species was first described as Mitra tuberosa Reeve, 1845, then moved to the genus Vexillum, where it became Vexillum tuberosum. More recently it has been demonstrated that it was not a Vexillum (it lacks lirations in the aperture) and it has been transferred back to Mitra, but some authors have forgotten to change ^tuberosum^ back to ^tuberosa^.
It is not true that all Latin plant names are feminine. For example, apium (parsley) is neuter and carduus (thistle) is masculine. Quercus (oak) is feminine because it is fourth declension. Botanists have the same problem with gender agreement that zoologists have.
About 95% of all molluscan genera that end in -us are masculine. Ficus and Venus are the commonest exceptions, being feminine. Some less common ones are Acus, Globivenus, and Bathydomus, also feminine.
Similarly, about 95% of molluscan genera that end in -a are feminine, but because -a is the commonest ending, there are lots of exceptions. Only a very few genera that end in -a are masculine: e.g., Argonauta and Amnicola, since nauta (sailor) and -cola (dweller) are masculine in Latin. Most of the exceptions come from Greek and end in the neuter -ma:
-derma (skin), e.g. Cerastoderma
-nema (thread), e.g., Didianema
-oma (bulge, tumor), e.g, Cyphoma
-poma (lid, i.e., operculum), e.g., Homalopoma
-ptygma (fold), e.g., Pleioptygma
-stoma (mouth), e.g., Calliostoma
-trema (hole), e.g., Cirsotrema.
However, -ma is neuter only about half the time, otherwise it is feminine, e.g., Agathatoma, Chama, Eulima, Gemma, Lima. The -um ending in Latin is always neuter.
Here are some guidelines for generic names ending with various letters:
-a, 95% feminine (see above for exceptions);
-e, 95% feminine;
-m, almost always neuter (I know of no exceptions);
-n, masculine or neuter, not feminine;
-o, masculine or feminine, not neuter;
-r, masculine about 60% of the time, can be feminine or neuter;
-s, masculine or feminine, rarely neuter;
-es, masculine; is, 80% feminine; -os, masculine; -ops, masculine; -opsis, feminine;
-x, almost always feminine;
any other letter, usually masculine.
Gary
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