9 



be inferred from the numerous closely-packed layers of 

 the petioles, each layer representing the successive 

 growths of the crowns of leaves, which adorned the 

 summit of the tree. The petioles are separated by a 

 thick ramentum, which forms the elevated margins, cir- 

 cumscribing the lozenge-shaped depressed areas which 

 were occupied by the petioles during the plant's life- 

 time. 



MANTELLIA NIDFOEMTS. Brongn. 



Cycadeoidea megalophylla. Buckl. 



Mantellia megalophylla. Bronn, 



Cycadites megalo])hyllus. Buckl. 



Zamites megalo])hyllus. Presl. 



Encejphalartos Bucklandii. Miq. 



Eclii}iosti]_)es nidiformis. Pomel. 

 Trunk cylindrical, permanent bases of the petioles 

 large, lozenge-shaped, two or three inches broad, by 

 one and a half deep, meshes in the woody cylinder 

 small and scattered. 



The height of our Portland fossil is five inches, its 

 breadth, including the cortical appendages, ten inches ; 

 a transverse fracture has removed a portion of the stem 

 below the summit, and exposes to view the internal 

 structure of the trunk. Through pressure its natural 

 cylindrical shape has become slightly elliptical, the 

 centre, which is composed of true cellular tissue, free 

 from separate woody bundles, and penetrated through- 

 out by gum canals, is an inch and three-quarters in 

 diameter, and circumscribed by a vascular band 

 traversed by medullary rays, an inch and a half across ; 



