The mamoncillo I am familiar with and grow has a hard peel , round and has orange pulp .
Sorry for being stubborn .
How is the Talisia esculenta ?
I am not sure how "hard" you mean by a hard peel. The spanish limes that I have had over the years have never had a hard peel. The peel was bit firmer than a lychee and longan peel but not hard like macadamia nut or something. The color of the pulp varies. I have seen a light creamish color to a more darker close to orange color as you described. The shape of the fruit also varies from oval to round. Some of the better cultivars from Puerto Rico are oval and not round.
The fruit definitely look over ripe, as you said, and that may explain the peeling of the seed coat.
Just in case it may be another species of Melicoccus, I looked through my entire Melicoccus and Talisia monograph that I have to verify.
It does not match:
M. espiritosantensis
M. pedicellaris
M. petiolulatus
M. oliviformis
M. antioquensis
M. novogranatensis
M. aymardii
M. lepidopetalus
M. jimenezii
The only species that it matches based on personal experience and the Melicoccus monograph seems to be M. bijugatus. I would have loved for it to be a different species because it is one of my favorite genera and I am hoping to get specimens of all of the edible species one day. Right now, I only have M. lepidopetalus and M. bijugatus. If you do happen to come across any of the other species, I am definitely interested in buying or trading for seeds.