This species, briefly referred to by Scott in 1909[250] and fully described in a recent paper[251], is founded on material from the Lower Coal Measures of Colne, Lancashire. It agrees in essential features with _Medullosa anglica_, but differs in the following particulars: the linear dimensions of the stem are about one quarter those of a typical stem of the older species; the leaf-traces possess little or no secondary xylem and the relatively large decurrent leaf-bases have a narrower and simpler hypoderm. The stem has a tri-stelar vascular system enclosed in a ring of internal periderm, and each stele (3 mm. in diameter) consists of a roughly triangular strand of reticulate tracheids and a small amount of scattered parenchyma. The protoxylem is either exarch or, as in _M. anglica_, mesarch, the exact position being difficult to determine in the available material. The secondary xylem closely resembles that of _M. anglica_. Scott suggests the possibility that _Alethopteris decurrens_ may be the foliage of _Medullosa pusilla_. It is possible that there is no specific difference between _M. pusilla_ and _M. anglica_, but on the present evidence the employment of a distinctive name is desirable. _Medullosa centrofilis_ de Fraine. This species was founded by Miss de Fraine[252] on a petrified stem from the Lower Coal Measures of Lancashire. The maximum diameter of the flattened stem including four decurrent leaf-bases is 5 cm. The vascular system consists of an outer group of four steles, reduced to three by fusion in the upper part of the specimen, enclosing a central smaller stele or star-ring (fig. 417). It is the presence of the star-ring that distinguishes this type from the other two British species and forms a connecting link with certain continental Medullosae. The peripheral steles agree with the steles of _M. anglica_ but, as in _M. pusilla_, there is some doubt as to the exarch or mesarch position of the protoxylem. In the structure of the xylem the central stele conforms to the rest of the vascular system and a strand of protoxylem is preserved that is almost certainly exarch. There is evidence that the peripheral steles occasionally anastomose, but the central stele follows an independent course at least in the piece of stem examined. Leaf-traces are furnished by the primary xylem of the outer steles, and they appear to be without secondary tracheids as in _M. pusilla_. A zone of secondary cortex encloses the vascular system as in the other British stems: it is pointed out by Miss de Fraine[253] that this tissue, usually described as a deep-seated periderm, must have differed from cork in that there is no sign of drying up or decay in the tissues external to it. The leaf-bases are of the usual _Myeloxylon_ type. In size this species is intermediate between _Medullosa anglica_ and _M. pusilla_.