Oligopygus putnami (Israelsky, 1933).
Matrix free well preserved test. on the edge of the upper surface there is a distinct depressed area of test where the Echinoid has been 'nibbled' by a predator. Probably a fish or shark. Unusual.
Upper Eocene.
Chispas, Mexico.
Echinoid : 2.9 x 2.2 x 1.3 cm.