DIOONITES. 39 



Dioonites, and gives the essential characters as follows: 1 "Folia 

 pinnata, pinnis pro more angustis, lanceolatis, acutis, obliquis, 

 tota latitudine insertis, basique leniter pro- et decurrentibus, 

 nervis parallelis." In Zittel's Handbuch* the genus is quoted, 

 and Pterophyllum Buchianum, Ett., and P. Brongniarti, Schenk, 

 are given as two typical species. The former of these has since 

 been transferred by Nathorst to a new genus, Zamwphyllum, 3 on 

 the ground that the pinnae are slightly narrowed towards the 

 base. Saporta repeats the character of Dioonites 4 as given by 

 previous writers, and figures D. Brongniarti as a typical example ; 

 but the species referred to by this writer at the end of his 

 definition as the typical form of the genus is D. Eurrii, Schiinp. 

 In Fontaine's Potomac Flora we find numerous forms included 

 under Miquel's genus, but it must be noted that this author, 

 while giving what he refers to as Schimper's definition of the 

 genus, speaks of the pinnae as "sometimes expanded at base so 

 as to extend up and down the rachis." 5 This is an important 

 alteration, as Schimper describes the pinnae as distinctly 

 decurrent, and it is this characteristic which is repeated by the 

 majority of writers as one of the essential generic features. In 

 his definition of Dioonites Buchianus (Ett.) Fontaine refers to 

 the pinnae as slightly narrowed at the base, but does not regard 

 this character as opposed to the adoption of Miquel's genus. The 

 attachment of the pinnae by the whole of a more or less 

 decurrent base appears to be the chief characteristic generally 

 insisted on. In several definitions of Dioonites no mention is 

 made of the place of attachment of the frond segments, whether 

 on the surface or sides of the rachis ; in several of the figured 

 specimens referred to this genus the pinnae are inserted laterally. 

 Some authors have emphasized the fact that the segments must 

 be attached to the upper surface of the rachis, as in D. Brongniarti. 

 This position of the pinnae affords one point of difference from. 

 Pterophyllum, and in the decurrent and separate leaves we have 

 other features characteristic of Dioonites. Nathorst, in discussing 



1 (A.), Trait, pal. veg. vol. ii. p. 128. 



2 p. 223. 



3 (A. 3), p. 46. 



4 (A. 2), vol. ii. p. 44. 



5 p. 181. 



