A, from the Inferior Oolite of Yorkshire (British Museum); B, from Jurassic rocks in Turkestan. ] Lower Cretaceous casts of tree-fern stems in the Prague Museum have been described under the names _Alsophilina_ and _Oncopteris_; the figures of the latter (fig. 276) given by Feistmantel[918] and by Velenovský[919] show the petiole-bases arranged in vertical rows and characterised by leaf-traces consisting of two separate strands in the form of two =V=s lying on their sides. Tree-fern stems described under various generic names are not infrequently found in European Lower Cretaceous rocks: their comparative abundance affords an example of striking changes in geographical distribution since the latter part of the Mesozoic epoch. The Cyatheaceae no longer exist in Europe and the arborescent species of the genus have retreated to more southern regions. [Illustration: FIG. 276. _Oncopteris Nettvalli._ (After Velenovský; ¾ nat. size.)] [Illustration: FIG. 277. _Protopteris punctata._ (After Heer; very slightly reduced.)] _Protopteris punctata_ (Sternb.). Fig. 277. The earliest information in regard to the anatomy of this widely spread Lower Cretaceous fern we owe to Corda, who showed that the species agrees in essentials with existing tree-ferns. The English example described by Carruthers[920] from Upper Greensand beds in Dorsetshire (now in the British Museum) shows only the external features. The sandstone cast (14 cm. in diameter), of which a portion is seen in fig. 277, was described by Heer from Disco Island (Greenland) as a Carboniferous species[921], but afterwards correctly assigned to the Cenomanian series[922] This species is recorded also from the Lower Cretaceous of Bohemia by Frič and Bayer[923] Among examples of petrified stems exhibiting a general agreement with _Protopteris punctata_ are those described by Stenzel[924] from Turonian rocks in Germany. In one of these, _Rhizodendron oppoliense_ Göpp., attention is drawn to branches given off from the stem stele which have a solenostelic structure in contrast to the dictyostele of the stem; also to the minute structure of the tracheae which appear to have their ends perforated, a feature shown by Gwynne-Vaughan[925] to be characteristic of the xylem elements of many ferns. [Illustration: FIG. 278. A. _Laccopteris polypodioides_, Brongn. [From a specimen (39275) in the British Museum; slightly reduced.] B. _L. Muensteri._ C. _Dicksonia_ (petiole stele). D. _Onychiopsis Mantelli_ (fertile segments). E. _Hausmannia Sewardi_ Richt. F. _H. Kohlmanni_ Bicht. G, H. _Protopteris Witteana_, Schenk. (x, xylem; R, roots.) (B, after Schenk; E, F, after Richter.)]