332 Systematic Paleontology 



two being continuous. The angle of divergence of the pinnae is of minor 

 importance since it will obviously vary greatly in proceeding from the 

 base to the apex of the frond. 



It may be unfortunate that the name suggests a relationship to the 

 modern genus Dion Lindley, but the time has passed when generic 

 names have other functions than mere names^ and the suggested relation 

 to Dion, if it is suggested, is not wider of the mark than the implications 

 of the term Zamites. The latter name is more properly retained for 

 frond types in which the pinnae are articulated to the rachis, often de- 

 veloping a prominent basal callosity and frequently found as detached 

 fossils, which is not the usual method of occurrence of Dioonites, in 

 which the pinnae, as might be imagined from their structure, are markedly 

 persistent. 



The genus is a widespread and characteristic member of the Wealden 

 and other Lower Cretaceous floras, and although Seward includes the 

 Cenomanian Pteropliyllum. saxonicurn of Reich in the synonymy of ■ 

 Dioonites Buchianus it is very doubtful if this species extends above the 

 Lower Cretaceous. In its typical form it is a very prominent element 

 in the oldest Potomac flora. 



Dioonites Buchianus (Ettingshausen) Bornemann 

 Plates LI, LII 



Pterophyllum Buchianum Ettingshausen, 1852, Abh. d. k. k. Geol. Reicli- 



sanst.. Band i, Abth. iii. No. 2, p. 21, pi. i, fig. 1. 

 Dioonites Buchianus Bornemann, 1856, Org. Rest. d. Lettenkohlengruppe 



Thiiringens, p. 57. 

 Dioonites Buchianus Schimper, 1870, Pal. Veget., tome ii, p. 149. 

 Pterophyllum Buchianum Schenk, 1871, Palseontograpliica, Bd. xlx, 1869, 



p. 8, pi. iii, fig. 5. 

 Dioonites Buchianus Fontaine, 1890, Mon. U. S. Geol. Surv., vol. xv, 1889, 



p. 182, pi. Ixviii, fig. 1; pi. Ixix, figs. 1, 3; pi. Ixx, figs. 2, 3; pi. Ixxi, 



fig. 1; pi. Ixxii, figs. 1, la, 2, 2a; pi. Ixxiii, figs. 1-3, 3a, 3b; pi. Ixxlv. 

 Zamiophyllum Buchianum Nathorst, 1890, Denks. Akad. Wiss., Wien, Band 



Ivii, pp. 46, 49, pi. ii, figs. 1, 2; pi. iii; pi. v, fig. 2. 

 Zamiophyllum Buchianum Yokoyama, 1895, Journ. Coll. Sci., Imp. Univ., 



vol. vii, p. 223, pi. xx, fig. 1; pi. xxiii, fig. 6; pi. xxvii, figs. 5a, b; pi. 



xxviii, figs. 1, 2. 



