Alti

The four parts of Trionfo del Tempo are for two sopranos and two alti.

Source: wiktionary

Another of his works which would be very attractive is the Psalm 23d for two soprani and two alti.

Source: wiktionary

The new chorus of angels, “Fear thou not,” for two soprani and two alti, is a smooth piece of devotional writing, excellently adapted to its position in the work, Peter’s air, “The heavens are opened,” with its appropriate harp accompaniment, immediately following it with increased effect.

Source: wiktionary

Points of special effect were the music—for two first trebles and two alti—in which Mendelssohn has wrapped the words of the heavenly voice, “Saul! Saul! why persecutest thou Me?” the drums at the opening of “Arise and shine,” the brass interludes (as well as the general grandeur) of “Sleepers wake”—surely the finest treatment of a choral known to music—the well-known violoncello accompaniment to “Be thou faithful” (rendered by Mr. Pettitt); and the always fresh grace of “How lovely are the messengers.”

Source: wiktionary