DBSCEirTION OF SPECIES. 157 



The form ami size of these leaves is so variable rlint at first sight they 

 appear referable to three or four different species. But in compariug the 

 characters in each of the leaves it does not seem possible to separate them. 

 Ill all of them the lateral primary nerves are supra-bastlar, having a pair of 

 thin, marginal veinlets underneath and distinct, except in Fig. 9. The 

 lobes, passing from those of the longer leaves (Figs. 1 and 2), where they 

 are very short and very obtuse, become longer and more ojien in Fig. 4, 

 and still longer and narrower in Figs. 3, 6, and 7, then enlarged at their 

 outer end, and there lobed, as in V\g. 5. 



The nervation being the same in all the leaves, the oiitlines are so 

 gradually iiioditied that the separation of one of them would necessitate 

 the admission of a specitic name for each. 



The most distinct in form are those of Figs. 8 and 9. Fig. 8, although 

 of tlie same type of nervation as the others, is, from the teeth of the upper 

 part, perhaps nearer to Parrotla (/randidentata of- PI. XX, but the nervation 

 is different. Fig. 9 has the secondaries basilar and no traces of a tliiii nerve 

 underneath. But the base of the leaf is curved into the stone and the gen- 

 eral character is the same as in Figs. 1 and 2. Differences of this kind are 

 often remarked in the leaves of living species of Acer. 



Tlie relation of this leaf is marked with Acer antiquum Ett.,' a leaf in 

 which the lateral jirimaries emerge from the base, though the subdivision of 

 the loljes is of the same character as in Fig. 7 of our plate. The author 

 compares his leaf to A. dccipicns Heer,'' a species with trilobate leaves, and 

 entire, acute or ai-umiuate lolies, the primary nervation basilar. Possibly 

 the supra-basilar nervation of these leaves might be considered as against 

 tlie reference of this species to Acer; but the same disposition is observed 

 in the primary nerves of a number of species of the genus in A. p.scudo 

 mouspessulanHm Ung. (Chlor. Prot., PL xliii. Fig. 2), A. pseudocampcsfrt' l"ng. 

 (ibid., Fig. 7), .1. ohtusilohum Ung. (ibid.. Fig. 12), species which have entire 

 leaves and like the Cretaceous leaves, sometimes a thin pair of basal nerves 

 under the primaries. Still the same character is seen in inanv of the leaves 

 tigured liy Ileer in his Fl. Tert. Helv., and especially in A. indirl'ium Web. 

 (Tertiarfl. Niederrh. Braunkohlenform., PI. v, Fig. 2), and A. ritifoVmm Lud- 

 wig (Foss. Pfl. Rhein.-Wett. Tertiar-Form., PI. mi. Fig. 1). Hence the 

 supra-basilar distribution of the lateral primaries can not eliminate these 

 leaves from the genus Acer. It is true that as yet, w ith the exception of 



' Kreidetl. v. Niederschoena, p. 259, PI. in, Fig. 17. 



*F1. Tert. Helv., vol. 3, p. 58, PI. cxvii, Figs. 15-22; Pi, clv, Fig. 12, 



