According to Worcester’s Dictionary (1860), an alco is “a kind of dog kept by the aborigines of the West Indies, allied to the Mexican mopsy”.
And while I’m at it, there’s an entry in the Century Cyclopedia (1880): Chinese Edible Dog. It was bred, as its name makes obvious, for the table in the Far East.
Are these breeds extant, maybe under a different name? Or are they lost to history?