here is a pic of one i had .
came into the shop as hystrix(even though they dont come from peru)
some people say they are juvenile yepezi , and the reticulated markings spread as they age leaving a sandy coloured backgraound with dark brown/green squiggles.
here is a link to another thread. http://www.monsterfishkeepers.com/forums/showthread.php?t=159715
which has pictures of the same type of ray as a juvenile and what they grew into. i have seen pics of this species around 24" across so not the snall hystrix type at all.