CUTICLES OF CTCADEAN FEONDS. 



193 



its characters the distinct cuticular structure and the dichotomising of some of the 

 secondary veins. In 1911, while working in Prof. Nathorst's laboratory, one of us was 

 able to re-examine his specimens and preparations, and found that one of Prof. Nathorst's 

 fronds, that figured on PL 6. figs. 23 & 25, was really a specimen of Iceniopteris 

 nittata, showing a forking venation. As this form yields good preparations it had been 

 used in the description of the examples figured on his PI. 7. fig. 21. 



M 



Prom tbe other specimen only very fragmentary preparations could he obtained, but 

 they were sufficient to show that their structure was quite distinct, agreeing with that 

 of true Nilssonias, in w^hich the cuticles are extremely delicate. In this form the 

 fragments of cuticle (one of them is shown in PI. 20. fig. 11) show that the upper 

 epidermis is composed of elongated rectangular or tapering cells, with straight walls 

 similar to those of N. medicma. The lower epidermis has fine rectangular or squarish 

 cells wdth straight walls and small dark rounded structures like the papillate hairs of 



N. compta and N. mediana. No stomata can be clearly seen. 



Other examples of the same kind have been obtained from the Gristhorpe bed ; they 

 agree in the characters given above, but do not add any information. They show a well- 

 marked minute wrinkling of the cuticular film which rather obscures detail. 



Prom these facts it appears that the name Nilssoniopteris must be abandoned, for the 

 cuticles of the Yorkshire specimens referable to Nilssonia orientalis {tenumervis) are 

 of the same type as those of other species of Nilssonia. 



Ctenis falcata, Lindl. & Hutt. 



Specimens of this species found in the Gristhorpe bed flake off very readily from the 

 matrix and yield fairly good cuticular preparations. 



The upper epidermis is very strongly cuticularised, and the thickening evidently 

 originally extended down the radial walls to a considerable extent, for the cell outlines 

 are now represented by thick badly defined lines of cuticle. The cells above the nerves 

 are especially strongly cuticularised, often causing the nerve-courses to stand out as 

 dark, slightly raised lines; only two or three rows of cells, however, are affected, and 

 not a broad series. The anastomosing of the veins is clearly shown on both the upper 

 and the lower cuticles. The cells of the upper cuticle are irregular in outline, but are 

 more or less isodiametric, varying between squares and hexagons. Some of tliem seem 

 slightly papillate, but are not markedly so. No stomata are present on the upper 

 surface. The lower cuticle (PI. 20. fig. 18) is somewhat similar to the upper in thickness, 

 but the cell outlines are larger and more distinct. The vein-courses are marked by a 



n 



more regular arrangement of cells, and the stomata occur somewhat scattered in the 



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enmg 



Their numerical distribution is from 60-70 per square mm 



As in Nilssonia, the guard-cells are sunk and are not clearly seen. The cells 

 surrounding the stomata-openings are not much differentiated in form or thickening 

 from the ordinary epidermal cells ; where they adjoin the guard-cells, however, there is 

 a solid ring of thickening round the stomatal cavity (PL 19. fig. 19). The latter is 

 apparently not very deep, and the guard-cells are often seen at its base. They are 



