Black beaded lizard

Why is it a ‘’beaded lizard’’ when it’s solid black? We have Mexican and Rio Fuerte beaded lizards in Philadelphia Zoo, what subspecies is this? Is it a Guatemalan beaded lizard?

@Kevin2342 I'm pretty sure that the subspecies is the black beaded lizard (hence, the title of the photo). After some quick research, it looks like it is also known as the Chiapan beaded lizard.

@Bisonblake yes, completely forgot about that species! Chiapan beaded lizard and black beaded lizard are the same thing. The website says the zoo only has Guatemalan beaded lizard but it may be outdated since indeed they have both subspecies.

@Bisonblake after some research, I can clearly distinguish all four species.
-The Mexican Beaded Lizard is the most well known and common species, it is normally brown with a bunch of yellowish spots spread throughout the body.
-The Rio Fuerte Beaded Lizard is a close relative to the Mexican beaded lizard, but it has a smaller range, darker coloration and less spots. The spots also tend to be more whitish and smaller than the Mexican.
-The Guatemalan Beaded Lizard is exteremely rare, with only a few hundred left. It is typically dark like the Rio Fuerte beaded lizard, but has more, larger spots.
-The Chiapan Beaded Lizard is found in southern Mexico, and is a dark gray-brown color with little to no spots. This species is also known as the Black Beaded Lizard. The name ‘’beaded lizard’ is misleading to this species, as it dosen’t have spots or ‘’beads’’.