DIOONITES. 43 



fig. 3 shows the pinnae apparently attached rather to the side than 

 to the middle of the upper surface of the rachis ; the bases are 

 slightly swollen, and the apices pointed. In pi. vi. fig. 4 of the 

 same author part of the broad rachis is shown, and the approximate 

 and narrowly linear pinnae are inserted at right angles to the frond 

 axis. The specimen figured by Dunker and named by Goppert 

 PteropJnjllum alietinum, bears such a strong resemblance to Dioonites 

 Dmikerianus as seen from the under side of the frond, that I have 

 ventured to insert this species as a possible synonym. Schenk has 

 previously called attention to this resemblance, and suggests that 

 possibly the similarity may amount to specific identity ; Schenk's 

 figure shows a distinct midrib in the pinnae, but this must be an 

 error in the sketch or some deceptive appearance in the fossil. 

 The specimen referred to Dioonites ahietinus, by Hosius and 

 von Marck, is probably a fragment of Zamites Buchianus (Ett.). 1 

 Schenk adopts Miquel's generic term Dioonites, which the latter 

 author proposed in 1851 for this and other species of Pteropliyllum. 

 In speaking of the genus Cycadites, reference was made to Schenk's 

 substitution of Dioonites or Pterophyllum for Cycadites, in the case 

 of certain specimens previously assigned by Dunker to the latter 

 genus; an examination of the type specimens having convinced 

 Schenk of the absence of a single median vein in the leaf segments, 

 and therefore of the erroneous adoption of the same Cycadites. 

 Schenk's figure 1, pi. xxxvi. 2 shows a portion of one side of 

 a frond with closely placed long and narrow pinnae, which in their 

 manner of attachment suggest a spirally twisted frond axis, such 

 as we have in the recent cycad Macrozamia spiralis, Miq. ; but this 

 may well be an accident of fossilization. Fig. 5 of Schenk shows 

 the same kind of rachis as in Dunker's fig. 4, pi. vi. The figures 

 of the epidermal cells given by this writer show a distinctly 

 undulating outline in the walls, and the presence of numerous 

 stomata. 



It does not seem quite clear whether Schenk has correctly 

 included C. Brongniarti, Rom., as a synonym of the present 

 species ; 3 he speaks of Homer's species as probably the upper 



1 (A. 1), Palseontographica, vol. xxvi. p. 213, pi. xliv. fig. 199. 



2 (A. 2), Palseontographica, vol. xix. 



3 Loc. cit. p. 233. 



