Calamites, extinct species of fossil plants, originally classed by most botanists as crypto-gamous, being regarded as gigantic equiseta. The horsetail of our marshes is a slender herbaceous plant, with a hollow stem and rarely more than two feet high: while the calamites of the carboniferous marshes had partly woody trunks, and some were 20 feet or more in height. Of the genus calamites about 50 carboniferous species have been described, only three or four triassic, two Jurassic, and none of later periods. Adolphe Brongniart has shown in his Genres de vegetaux fossiles (1849) that many calamites cannot belong to the equi-seta, nor probably to any tribe of flowerless plants. He conceives that they are more nearly allied to the gymnospermous dicotyledons. Prof. Williamson, on the contrary, thinks that in the arrangement of their tissues they differ widely from all known forms of gymnosperms. These remarkable plants unfortunately possessed very delicate tissues, so that perfect specimens are extremely rare, and hence the uncertainty respecting them.