XXXIX] ZAMITES 531 



fronds with pinnae attached to the upper face of the rachis with 

 a contracted and always symmetrical base though in some cases 

 the basal contraction is exceedingly small; there is a more or 

 less distinct basal callosity. He recognises two types, (i) Eu- 

 Zamites, e.g. Zamites gigas (fig. 599), in which the pinnae are strongly 

 contracted basally and have a callosity, and (ii) Sub-Zamites, 

 e.g. Z. borealis^, etc., in which the pinnae are not so broadly rounded 

 at the base and retain the same breadth to the point of insertion 

 where they are 'very rapidly and very little contracted,' with 

 or without a basal callosity. The basal callosity in these forms 

 is not shown in many of the pinnae and is at most but a sUght 

 rounding of the angles of the truncate base. The specimens 

 referred by Halle to Sub-Zamites do not appear to differ in any 

 feature worthy of generic rank from Ptilophyllum. 



In the following definition Zamites is employed in a sense more 

 or less in accordance with Brongniart's usage but with the inclusion 

 of such forms as Z. Buchianus, the type of Nathorst's Zamiophyllum, 

 and the exclusion of Heer's Arctic and Halle's Antarctic fronds 

 referred by them to Zamites. 



Fronds broadly lanceolate reaching a length of over 60 cm. ; 

 pinnae more or less oblique or at right-angles to the rachis (fig. 

 599), attached to the upper surface but not completely covering 

 it, linear or linear-lanceolate, acuminate or obtuse, usually abruptly 

 contracted at the rounded base and more rarely {e.g. Z. Buchianus, 

 fig. 601) gradually tapering to the proximal end, with or without 

 a callosity at the symmetrical base ; veins divergent at the base, 

 simple or dichotomously branched, for the most part parallel to 

 the edges of the lamina and slightly divergent in the apical region. 

 The presence of a basal callosity, such as is best seen in the pinnae 

 of recent species of Macrozamia, is not a feature of great im- 

 portance and cannot be easily recognised in many impressions. 

 In the process of fossilisation the pinnae are often flattened against 

 the surface of the rachis and this may produce transverse wrinklings 

 of the lamina suggestive of a basal thickening. In some cases 

 stems of the BucJclandia type occur in connexion with Zamites 

 fronds (fig. 541). An account of these stems, and of inflorescences 

 of WilUamsonia which were borne by some at least of the plants 



1 See page 525. 



34—2 



