Komentaryong Sumisipi para sa Mga Awit 76:10

עגלות, seeing that the word is in a construct mode, i.e. עגלות צב, the vowel pattern is “eglot,” “draught carts”, instead of “agalot,” “carts.” We know similar vowel pattern changes in the word “essrot,” “tens of,” instead of simply assarot, tens. When the Torah writes that “one” cart was brought by a team of two princes it uses the standard vowel pattern agalah, as in that part of the verse the princes are the adjective (so to speak) and not the carts, as in the beginning of the verse.