378. In this declension

In this declension, masculines and feminines of the same final are inflected alike; and neuters are peculiar (as usually in the other declensions) only in the nom.-acc.-voc. of all numbers.

a. The majority of consonantal stems, however, are not inflected in the feminine, but form a special feminine derivative stem in ई ī (never in आ ā), by adding that ending to the weak form of the masculine.

b. Exceptions are in general the stems of divisions A and B — namely, the radical stems etc., and those in as and is and us. For special cases, see below.