The skate egg case is normally a one-embryo container. Yolk supply, capsule volume and gas exchange all scale to a single developing animal, and the case is sealed for months while the embryo consumes its yolk sac.
Big skate cases break that pattern. They are among the largest produced by any skate, reaching roughly 20 to 30 centimetres in length, and hold multiple embryos, commonly three or four, with counts as high as seven reported. Each young animal has its own yolk sac inside the shared capsule.
What this buys the species is not settled. Packing several embryos into one large case may reduce the total surface exposed to predators and fouling for a given number of young, or it may simply reflect a scaling of capsule production in a large-bodied skate. Only one close relative, the mottled skate of the northwest Pacific, is known to do anything similar.