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In 1872 I described (‘Phil. Trans,' 1873, “On the Organisation of the Fossil Plants of the Coal-Measures—Part IV.”), under the name ofHeterangium Grievii , one of the most interesting of the various plants which I discovered in the Burntisland deposit of Carboniferous limestone at Kinghorn. More recently we have obtained, from the Halifax beds, a very distinct plant, which, though differing in many important features fromH. Grievii , resembles it so closely in others that I propose to include it in the same genus, under the name ofHeterangium Tiliæoides . Its central medullary axis, A, differs in no conspicuous manner from that ofH. Grievii when transverse sections of the two are compared. Fig. 1 represents such a section enlarged 15 diameters, the medullary portion being seen at A, and a similar section is shown at fig. 2, A; whilst fig. 3 represents a small portion of a section enlarged 103 diameters. From the latter of these sections it will be seen that this medullary axis consists of irregular clusters of vessels or tracheids,b , the intervals between which are filled with ordinary parenchyma,a . The vessels near the periphery of this axis are smaller than those constituting the more central bundles—a feature best shown in fig. 2,b '. The character of these vessels will be referred to immediately.

XII. On the organisation of the fossil plants of the coal-measures.—Part XIII. Heterangium tiliæoides (williamson) and kaloxylon hookeri