placoids

As the rays and sharks both belong to the order of placoids, it appears that the shark is not particular about preying on his kindred.

Lippincott's Magazine of Popular Literature and Science Volume 12, No. 33, December, 1873 Various

We do not see a sturgeon (our British representative of the ganoids) once in a twelvemonth; and though the skate and dog-fish (our representatives of the placoids) are greatly less rare, their number bears but a small proportion to that of the fishes belonging to the two prevailing orders, of which thousands of boat-loads are landed on our coasts every day.

The Testimony of the Rocks or, Geology in Its Bearings on the Two Theologies, Natural and Revealed Hugh Miller 1829

The earliest fishes -- firstborn of their family -- seem to have been all placoids.

The Testimony of the Rocks or, Geology in Its Bearings on the Two Theologies, Natural and Revealed Hugh Miller 1829

The Port Jackson shark, however, -- a creature that to the dorsal spines and shagreen-covered skin of the common dog-fish adds a mouth terminal at the snout, not placed beneath, as in most other sharks, and a palate covered with a dense pavement of crushing teeth, -- better illustrates the order as it first appeared in creation than any of our British placoids.

The Testimony of the Rocks or, Geology in Its Bearings on the Two Theologies, Natural and Revealed Hugh Miller 1829