Disk small, membranous, often indistinct, a character which separates this genus from Ophiura. Rays very long, slender, depressed, formed of circles of plates, four in each circle; the lateral plates are the largest, most prominent, and provided with long spines; the basal plates are small and spiniferous, and the dorsal smooth and without clothing. Mouth plates small and triangular. All the species known have been found in the Jurassic rocks.