532 CYCADOPHYTAN FBONDS [CH. 



with Zamites leaves is given in Chapter xxviii. In such examples 

 of Zamites as have been examined the epidermal cells have sinuous 

 walls and the stomata^, confined to the lower face of the lamina, 

 occur in rows with their long axis at right-angles to that of the 

 pinnae. 



Zamites ranges from Rhaetic to Lower Cretaceous strata. 



Zamites truncatus ZeiUer. 



A Ehaetic species from Tonkin ^ characterised by oval linear 

 pinnae given ofi at a wide angle, alternate and not contiguous; 

 apex obtusely truncate, gradually narrowed to a cimeate base 

 which is rounded or elliptical and has a more or less definite 

 callosity. The pinnae vary from 3 to 5 cm. in length and from 

 5 to 13 mm. in breadth. 



Zamites gigas (Lindley and Hutton). 



The specific name gigas is retained in preference to that of 

 Mantelli employed by Brongniart* on the ground that he after- 

 wards discarded it in favour of the designation proposed by 

 Lindley and Hutton*, and because their name has been generally 

 adopted. 



Fronds large, exceeding 60 cm. ; broadly linear lanceolate ; 

 the comparatively slender rachis bears alternate linear lanceolate 

 pinnae with a rounded and usually slightly swollen base and an 

 acuminate apex. At the apex of the frond the pinnae are narrow 

 and linear (fig. 599) and almost parallel to the rachis; in the 

 lower part they are shorter and relatively broader and attached 

 approximately at right-angles. The numerous veins diverge from 

 the centre of the base but for the most part are parallel to the edge 

 of the lamina. The form of the epidermal cells and the structure 

 of the stomata have recently been described by Mr Thomas. 

 The external features of the stem (fig. 541) are described under 

 the genus Williamsonia. In the case of fronds of this type 

 from English Jurassic rocks it would be legitimate to speak of 

 them as Williamsonia gigas, but in view of the fact that such 



1 Thomas and Bancroft (13) p. 184. 



2 Zeiller (03) B. p. 166, PL xiin. figs. 3—6. 



2 Brongniart (28) A. p. 94. See Seward (00) B. p. 178. 

 * Lindley and Hutton (38) A. PI. clxv. 



