336 L. F. Ward — Fossil Cycads in the Yale Museum. 



Cycadeoidea rhombica n. sp. 



Trunks of medium size (40-50 cm high, 20-30 cm in diameter), 

 subcylindrical, tapering upward, more or less laterally com- 

 pressed, unbranched ; rock soft on the immediate surface, hard 

 and flinty within, reddish brown on the weathered surfaces, 

 whitish and somewhat chalcedonized in the interior, with rather 

 high specific gravity; organs of the armor horizontal or some- 

 what descending ; phyllotaxy clear and well marked, the spiral 

 rows from left to right forming an angle with the axis of 25°, 

 those from right to left of 60° ; left scars strictly rhombic with 

 parallel sides and all angles, vertical as well as lateral, sharp, 15 mm 

 wide, 9 ram high, and very uniform ; leaf bases present usually fill- 

 ing the scars, square across the top but lying at different levels, 

 rough-granular and somewhat porous, without apparent bundle 

 scars ; walls very thin, rarely l mm , consisting of a white flinty 

 substance, the surface smooth and longitudinally grooved or 

 pitted, often not rising to the summit of the leaf bases, thus 

 forming cracks between them, often split into two, more or 

 less equal, thin plates; reproductive organs present but not 

 specially numerous or conspicuous, fairly well developed, 

 usually projecting or forming elevations, but occasionally 

 decayed, leaving cavities, small, 15x25 ram in diameter or 

 smaller, the involucral bract scars inconspicuous, the central 

 portion solid and amorphous externally; armor very thin, 

 15-20 mm , joined to the axis by a more or less irregular line some- 

 times appearing definite; woody zone about 4 cm thick, usually 

 showing three distinct layers ; cortical parenchyma 12-15 mm 

 thick, often conspicuously marked by the thick vascular bun- 

 dles passing across it and curving upward and outward to the 

 leaf bases, its outer wall marked by shallow, longitudinal 

 grooves, 6-10 cm long, pointed at their extremities, lying side 

 by side but overlapping one another ; fibrous zone in two 

 distinct rings, the outer 10-15 mm thick, the inner 12 mm thick, 

 separated from the outer by a definite line appearing on the 

 fractures as a seam or crack, its inner wall also definite, both 

 rings appearing longitudinally striate on radial fractures, but 

 both, and especially the outer, showing on transverse fractures 

 a radiate structure with woody wedges ; medulla 6-8 cm thick, 

 porous in its outer, and cherty or flinty in its inner, portion. 



This is one of the best-defined species in the collection, 

 although none of the specimens are complete. It consists of 

 Nos. 620, 623, 627, 629, 630, 631, and 640, all from the 

 Blackhawk region. These specimens all came in the same box 

 with a number of others of different species (C. Jenneyana 

 and C. ingens), and it seems probable that they were found 

 close together. Still a comparison of them shows that they 



