family Asterotrygonidae for convenience, with Asterotrygon maloneyi as the type species. It is diagnosed from other myliobatoid families by the combination of characters given in such study. This is the species previously referred to as the undescribed ray or the fat tailed ray, and was not officially described and named until 2004. It is easily distinguished from Heliobatis in its having a dense covering of skin denticles, some of which bear curved, hook-like spines. It also has a fat tail covered with small bony plates known as dermal denticles. The tail of Asterotrygon was probably not quite as flexible as the whip tail of Heliobagis, and a dorsal fin just anterior to the stings. Asterotrygon is known only from the FBM deposits, where it is very rare. It is estimated that it is about 40 times rarer than Heliobatis. References Myliobatiformes Eocene fish Eocene fish of North America