Abstract: The present paper deals with the cuticular structure of some specimens of Thinnfeldia rigida Sze (Pl. Ⅰ, figs. 1–6b), collected from the upper part of the Yenchang formation (Upper Triassic) in Zungaria of Inner Mongolia. The cuticles are very thick. The upper and lower cuticles of the leaf are rather similar (Pl. Ⅱ, fig. 3). The leaf is amplistomatic, but the frequency of stomata on one side, presumably the upper, is smaller than that of the other side. The shape of epidermal cells of the upper side (Pl. Ⅱ, fig. 1) are partly elongate-polygonal and partly isodiametric, while that of the lower side (Pl. Ⅱ, fig. 2) is mostly isodiametric. All the epidermal cells are straight-walled, and usually possess a median round hollow papilla (Pl. Ⅱ, fig. 5). In the elongate-polygonal cells, the papilla is also slightly elongate, but usually shifted to one end of the cell. The course of the veins is indicated by rows of elongate cells in the lower surface, but no clear indication of veins is given in the upper. There is a row of isodiametric cells along the margin of the upper cuticle of the leaf. Next to this row are 2–4 rows of elongate cells, regularly arranged, with their long axis perpendicular to the margin. Within these, there are 4–12 (mostly 6) rows of isodiametric cells, irregularly arranged. The thickness of the cells is 0.6–0.7μ. The epidermal cells of the upper cuticle measure 4.4μ × 2.2μ to 6.1μ × 2.1μ, while those of the lower 3.8μ × 3.7μ to 3.8μ × 3.4μ. The stomata are evenly scattered and irregularly orientated. They are haplocheilic and unicyclic (partly dicyclic) (Pl. Ⅱ, figs. 4-5). The guard cells are sunken and thinly cutinized. The inner aperture is 0.8-0.7μ in diameter, and the outer is 1.6-l.5μ. The guard cells are surrounded by a ring of 4-6 subsidiary cells, which are usually heavily cutinized, each bearing a long papilla directed inwards over the stomatal aperture. The encircling cells are almost indistinct, though occasionally recognizable from the ordinary epidermal cells. The cuticles of Thinnfeldia have been studied by Antevs, Gothan, Harris, and Lundblad, all being of a similar structure; namely, the arrangement of the subsidiary cells seems rather regular, and a thin stripe is usually present in the subsidiary cells. Some specimens possess slight papilla-like thickenings in the epidermal cells while others not. In the present specimens, the general structure of the cuticles is similar to them, but there is no indication of thin stripe on the subsidiary cells. Furthermore, the arrangement of the subsidiary cells in ours is rather irregular and tile papilla of the epidermal cells is better developed.