78 ZAMITES. 



fronds of which the obliquely inclined pinnae have a somewhat 

 narrowed base. This decrease in breadth towards the point of 

 attachment of a pinna is characteristic of numerous species of 

 Zamia, Ceratozamia, and Maerozamia, and might well be included 

 in a more extended definition of Zamites. The basal contraction 

 of the segments is, as Nathorst points out, directly opposed to 

 the accepted definitions of Dioonites and Pterophyllum but there 

 seems no good reason to regard such a feature as at variance 

 with the genus Zamites. This name Zamites was proposed by 

 Brongniart at a time when only two genera of living cycads 

 had been recognized, Cycas and Zamia ; and the present definition 

 of the genus stamps it rather as a comprehensive and provisional 

 designation for certain frond characters which are now shared 

 by various members of the recent Zamicce. If we retain Zamites 

 as usually defined, or in a slightly modified form, it must be 

 regarded merely as a convenient terra to be applied to certain 

 fossil fronds in which some of the characteristics of Zamia, 

 Maerozamia, Ceratozamia, or even Encephalartos may be repre- 

 sented. In the recent Zamia the pinnae are articulated to the 

 rachis, and in many forms are readily detached, leaving a distinct 

 circular or elliptical scar ; this same character is also met with 

 in other genera, such as Ceratozamia, Encephalartos, etc. The 

 basal callosity often referred to as one of the important charac- 

 teristics of Zamites is best seen in some forms of the genus 

 Maerozamia, and the manner of insertion and position of the 

 pinnae on the rachis in species of Zamites find a parallel living 

 in species of Encephalartos, Ceratozamia, Maerozamia, and Zamia. 



The following general definition of Zamites may serve to 

 indicate those characters which are most readily recognized in 

 fossil fronds : 



Frond pinnate, pinnae more or less obliquely inclined to 

 the rachis and attached to the upper surface, apices acuminate 

 and tapering, or obtusely rounded, the base may be abruptly 

 rounded and marked with a callosity near the point of attach- 

 ment, or the pinnae may be slightly and gradually narrowed 

 towards the base, margins entire ; veins parallel, but slightly 

 divergent in the apical portion of each pinna. 



Such a definition is perhaps suggestive of a genus with 

 characters expressed in too general terms, and not sufficiently 

 limited, but a more complete examination of the different types 



