The three-bar first phrase focuses on the upper fourth of the tonic octave, or D5-G5. The latter is the first note of a traditional Urlinie of the mirror form, ^8 down to ^5, then rising again to ^8. I have reproduced a figure from the introduction to this series; the form LeRoux uses for his "Piece sans titre" is boxed. To date, this is the only piece I have found using this Urlinie in the minor key. (It is actually fairly common in the major key.)
At (a) is ^8 of the Urlinie; a line will descend from it in section B. At (b) is the middleground line that covers section A, up to the PAC in the dominant. At (c) is an internal third-line that reaches D5 "early" and helps to expand the phrase to 6 bars.
The upper voice in phrases 3, 4, and 5—the first half of the B section—traverses a fifth-line from a superimposed inner voice at the beginning (A4 becomes A5 in phrase 3) eventually back to ^5 (by the middle of phrase 5).
Phrase 6 takes the line back up from D5 to G5 with a PAC as close. (The harmonies might suggest the F# on beat 1 as ^#7 better than beat 4, as I have it now.)
But the piece is not finished. A firm, apparently conclusive PAC on the tonic before the end is common in French harpsichord music because of the performance tradition of the petit reprise, in which the final phrase of a piece was repeated, presumably with additional embellishments or textural changes. In several pieces for the 1705 collection, LeRoux takes advantage of this tradition to add new music after the tonic close. In this case, he adds two phrases, the first of which picks up the figure of phrase 2—see phrase 7, where the figure is put into sequence. Phrase 8, then, starts from Bb5 as ^3 and brings the piece to a close with another firm cadence. I am not particularly fond of those Schenkerian readings that only reach their supposedly principal melodic tone near the end, and in this case it would make little sense anyway, as phrases 7 & 8 are in the petit reprise or coda-like region of the piece.
