82 ZAMITES. 



In the specimen represented in pi. v. fig. 1 of Nathorst, there 

 appear to be two elliptical scars about the middle of the frond 

 fragment ; these agree very closely with similar scars in several 

 of the Rufford examples, and represent the points of detachment 

 of pinna3. The abundant examples in the National Collection 

 enable us to extend and modify the existing definition of the 

 species. Among recent species Ceratozamia mexicana, Brong., 

 Zamia cycadifolia, Jacq., Macrozamia Macleayi, Miq., and Enceplia- 

 lartos Lehmanni, Lehm., may be mentioned as possessing fronds 

 very similar in form to those of Z. Buchianus (Ett.). 



We may define the species as follows : 



Frond large, pinnate ; rachis longitudinally striated, with a 

 fairly broad median groove on the upper surface. Pinnse 

 alternate, opposite or subopposite, varying in length from 3-4 cm. 

 to 20cm., and in breadth from T5 to 2mm., attached obliquely to 

 the rachis, and slightly thickened and somewhat broadened at the 

 actual point of insertion ; separated from the rachis by a distinct 

 absciss line, leaving an elliptical scar ; generally nai-rowed towards 

 the base, but in the narrower pinna? this reduction in breadth 

 decreases and is not nearly so evident ; usually inclined at about 

 45 to the rachis, they may be almost at right angles to the frond 

 axis, and in the case of young fronds and the apical portions 

 of larger ones, the pinna? are attached at a much more acute angle. 

 The distance between the pinna3 varies considerably in different 

 parts of the same leaf, and in leaves of different ages ; apices 

 generally tapering to a point, or more or less obtusely rounded. 

 Yeins numerous, parallel, and as a rule not very prominent. 



V. 2120. PI. VIII. 1 Fig. 1 and PI. III. Fig. 5. This splendid 

 specimen has a length of 77'5 cm. ; broken at one point, and 

 somewhat displaced laterally. Breadth of pinna? varies from 2 to 

 9 mm. Attachment of the pinnae not shown in this example. 

 The broader and lower pinna? appear to taper towards the rachis 

 more than in many specimens. Tips of some of the pinna? clearly 

 seen, as in PL III. Fig. 5 ; these agree very closely with the 

 apices of pinnae in V. 2123 (PI. III. Fig. 3). Certain parts of 

 this frond agree exactly with V. 2925, etc. The apical portion 

 appears to be identical with Dioonites Buchianus var. anffustifolia, 

 as figured by Fontaine in his pi. Ixx. fig. 2. 2 The lower portion 



1 Bepresented in PI. VIII. nat. size. 



2 Potomac Flora. 



