The Allen and Greenough is still under construction;
so some links may not work quite the way you would expect.
87. Neuter are nouns in -a,
-e, -l, -n, -ar, -ur, -us: as, poéma, mare, animal, nómen, calcar,
róbur, corpus; also lac and caput.
Exceptions are the following: -
a. Masculine are sál, sól, pecten, vultur, lepus.
b. Feminine is pecus (gen. -udis).