XXI.—Contributions to the Study of the Old Red Sandstone Flora of Scotland. III. On Hostimella (Ptilophyton) Thomsoni, and its Inclusion in a New Genus, Milleria. IV. On a Specimen of Protolepidodendron from the Middle Old Red Sandstone of Caithness. V. On the Identification of the Large “Stems” in the Carmyllie Beds of the Lower Old Red Sandstone as Nematophyton

Abstract

In a preceding paper of this series it was pointed out that the smooth branched axes, which are so common in the Middle Old Red Sandstone of Scotland, cannot be assumed to belong to one kind of plant. They were therefore for convenience referred to as Hostimella sp. It was further shown that three distinct types of sporangia were associated with axes of this general type and, on the characters afforded by the reproductive organs, three species were distinguished. These were provisionally retained under the generic name Hostimella, as H. pinnata, H. globosa, and H. racemosa. In the same paper it was mentioned that the linear bodies borne on the peculiar fossil known as Ptilophyton Thomsoni, Dawson, were almost certainly sporangia. This afforded another reproductive structure borne on a vegetative region, which, if found separately, could only be placed in Hostimella sp. Since, as had been pointed out by Kidston, the generic name Ptilophyton is inadmissible for this fossil, it was placed in the purely provisional genus Hostimella as H. Thomsoni. In the present paper the nature of this interesting member of the Scottish Middle Old Red Sandstone Flora will be more fully considered.