Abstract
A new species of Trigonocarpus Brongniart is described from the level of the Herrin (No. 6) Coal (Carbondale Formation, Kewanee Group) at Carterville, Illinois. The seed is three dimensionally preserved by authigenic cementation and exhibits a well preserved nucellar cast, integument and micropylar region. The specimen represents the largest pteridosperm compression‐impression seed collected in North America and measures 10 cm from the apex of the micropyle to the chalazal end, and at least 5 cm in breadth. Trigonocarpus leeanus sp. n. is compared to the remaining forty‐three taxa within the genus, and specifically with Trigonocarpus grandis Lesquereux, the one species with dimensions approaching it. An emended diagnosis, with designation of a lectotype, is presented for Trigonocarpus grandis. Correlation of the features displayed by Trigonocarpus leeanus sp. n. and the petrified taxa within Pachytesta Brongniart is attempted.
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