The generic name _Trigonocarpum_ was instituted by Brongniart in 1828[329] for ovoid longitudinally ribbed ‘fruits’ from Upper Carboniferous strata, the type-species being named _T. Parkinsoni_. The generic name is often altered to _Trigonocarpon_: Williamson[330], who adopted this form, states that Brongniart substituted _Trigonocarpon_ for _Trigonocarpum_ in his _Tableau_[331], but in that work the original termination is used, the form _Trigonocarpon_, probably the result of a slip, appearing only in the index. In his later work on seeds Brongniart adopted the name _Trigonocarpus_, and in recent years this has been widely employed. Among other species named by Brongniart are two previously referred by Sternberg to _Palmacites_. Several examples of Brongniart’s genus were described by Lindley and Hutton, and in their description of _T. Noeggerathii_ the statement is made that a fractured specimen demonstrated that ‘the fossil in its ordinary state is an interior part divested of fleshy covering’[332]; this suspicion of the true nature of the nut-like fossils was afterwards proved correct by the investigations of Hooker and Binney[333] and by the later work of Williamson. The specimens on which the genus was founded are casts of seed-cavities and it is in this state that the seeds are usually preserved, often in large numbers, in the sandstones of the Coal Measures, as in the block shown in fig. 423 from the famous quarry at Peel near Bolton, Lancashire. Another type of preservation is represented by the seeds figured by Lindley and Hutton as _Carpolithes alata_[334], but the generic identity of the two states was not recognised until the discovery of petrified material afforded the clue. Figs. 424, 1, 425 illustrate the appearance of _Trigonocarpus_ when preserved as a carbonised impression showing a thick fleshy envelope enclosing an oval kernel with a hard wall prolonged upwards as a longer or shorter micropyle. Casts of the seed-cavity are represented in figs. 423; 424, 2, 3. The surface of these casts occasionally shows one or more short cylindrical projections which are probably extensions of the sand or mud into holes formed in the testa by boring insects. The view that _Trigonocarpus_ seeds are ‘obviously Palm fruits’ was not accepted by Hooker and Binney who inclined to regard them as the seeds of Conifers and compared them especially with the similar nuts of _Ginkgo_ seeds (_cf._ fig. 631, C). It was Mr Wild[335] who was first struck by the association of _Trigonocarpus_ and the petioles of _Medullosa_ (_Myeloxylon_) and by some resemblances in structure between the testa and the hypoderm of the petioles; though, as Scott and Maslen[336] point out, the agreement is not so close as Wild believed, his view of a possible connexion between the reproductive and vegetative organs has been confirmed. Williamson extended our knowledge of the genus by his account of _Trigonocarpus olivaeformis_ Lind. and Hutt., a form