Matt, I think this answer needs to be revisted. I promise to put my thinking cap on squarely.

Looking back, I regret my "agree." I wasn't paying attention. We all missed the fact that the references to "bases" in the examples were plural and should have yielded the plural of basIs, i.e. basEs in the answer.

There are lots of *solid* refernces to "lexical base" on the Internet, whereas the references for "lexical basis" didn't appear to be relevant. The following passage convinced me that your text is, in fact, about lexical "base":

1. The Four Types of Lexical Derivation
1. Functional Derivation.
**The feature inventory of a lexical base is the list of features associated with it. These features are markers of the grammatical and semantic categories to which the base belongs**, e.g. ^Noun, ^Animate, ^Feminine. Functional lexical derivations insert a grammatical category function, like Subject (baker), Object (drawing), Instrument (can-opener), Location (bakery); among the feature inventory of the lexical base. **The relationship of the noun to the verbal lexical base in carver is that of the Subject of a sentence, i.e. a carver is "someone who carves", etc.** The relationship in carving is that of the Direct Object, i.e. a carving is "something which is carved" and an employee "someone who is employed". The relationship in writing as in writing paper is that of Purpose, a common function of the Dative case.
www.departments.bucknell.edu/Linguistics/lectures/05lect10....