260 Mr Hamshaw Thomas, On some new and rare ' 
: 
above the veins, stomata present in areas between the veins. 
Papillae absent. Lower epidermis smooth. Papillae only on 
subsidiary cells of stomata. Stomata small and not very 
numerous. 
Relationship with other forms. 
The genus Hretmophyllum, as has been already mentioned, 
possesses a number of features in common with the leaves of 
Ginkgo and must undoubtedly be classed among the Ginkgoales. 
The points of resemblance may be here summarised. Leaves 
broadest towards the apex, the lamina merging gradually into 
the petiole at the base, apical portion sometimes with a notch. 
Margins of the leaf thickened at the base. Veins distant, dicho- 
tomising. Secretory tracts between the veins. Epidermal cells 
rectangular or polygonal, their walls sometimes slightly sinuous. 
Stomata with sunken guard cells surrounded by five to seven 
somewhat thickened subsidiary cells arranged in a regular radial 
series. 
The leaves differ from those of Ginkgo in being oblanceolate 
or linear, but approach those of Ginkgodiwm in outline. Many 
examples of the latter have been figured by Yokoyama* and I 
have also described specimens from South Russia-F which may be 
referred to the same genus. Ginkgodium, however, is distinct in 
possessing shorter and comparatively broader leaves often deeply 
divided at the apex. A much more important distinction is seen 
in its nervation, the veins being fine, very numerous and parallel 
instead of spreading, they occasionally fork but do not converge 
at the base of the leaf, apparently springing from the thickened 
margin; interstitial nerves occur, but the venation is entirely 
different im character from that of the present genus. 
In their form, their slightly faleate shape, and to some extent 
in their nervation, my leaves resemble those of Feildenia described 
by Heer? from the Miocene of Grinnell Land. The leaves of this 
genus, however, differ considerably from mine in their smaller size, 
closer venation and less distinct petiole. Feidldenia Mossiana Hr. 
in its more ovate shape and coarser venation is the most com- 
parable, but the curious convergence of the veins at the apex (if 
correctly figured) is very distinct. The veins in Hretmophyllum 
usually converge somewhat at the apex but never join in any 
way resembling Heer’s figure§. 
Fontaine|| has figured a leaf of somewhat similar character to 
* Yokoyama (89), p. 56, Pl. 1. fig. 4c, m1, 7, vit., rx. 1—10, xir. 14, 15. 
* Thomas a), Pl. iv. figs. 9-11. 
+ Heer (78), p. 21, Pl. 1. figs. 3—11, vim. 2a, 3a, 4, 5. 
§ Idem, Pl. vit. figs. 2a, 3a, 4. 
|| Fontaine (89), Pl. uxxxv. figs. 5, 5a. 
