The finback catsharks, Proscylliidae, are a small family of ground sharks. They can be found in warm seas all over the world and are often the most numerous and common shark in tropical regions. They are generally less than 3 ft long, and are slow-moving predators that feed on bony fish and small invertebrates. Although some bear live young, the majority lay eggs with almost fully developed young; these egg cases, known as "mermaid's purses", are unique in appearance to each species.