On a new pygasterid (Echinoidea) from the Jurassic (Middle Lias) of Nevada, U.S.A.
Wanda Jesionek-Szymańska
Acta Palaeontologica Polonica 15 (4), 1970: 411-419
Plesiechinus hawkinsi n. sp. from the Middle Lias of Nevada, U.S.A., the oldest and most primitive representative of an irregular echinoid family of the Pygasteridae Lambert, 1900, displays a "regular" apical system with genital 5 perforate. Crenulate tUbercles in the new species contest earlier opinions on the derivation of pygasterids from echinoids with smooth tubercles.
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