104 THE LATER EXTINCT FLORAS OF NORTH AMERICA. 



spring seven or eight pairs of lateral nerves above the basilar pair; these 

 diverge at an angle of about 35 degrees, are slightly flexed at the base, 

 straight or nearly so above, where they are somewhat truncated, their 

 branches terminating' in the marginal teeth. The basilar nerves diverge 

 from the midrib at an angle of about 35 degrees and run nearly straight to 

 the extremities. of the lateral lobes. They each give off on the lower side 

 seven or eight branches, of which the second or third is strongest. These 

 are more or less curved and branched, the branches terminating in the teeth 

 of the margin. Fruit two to three lines long, prismatic, clavate." 



Collected by Dr. F. V. Hayden. 



This fine species, which is well represented in the collection, is closely 

 related to Platanus aceroides, so common in the Miocene strata of Europe. 

 There are, however, noticeable differences, which seem to me to have a 

 specific value. The leaves of P aceroides, though exhibiting a great variety 

 of form, are, I believe, always acutely toothed, while in the specimens 

 before us the teeth are never acute, except those which in the young leaves 

 represent the lateral lobes of the mature form. In P. aceroides also, accord- 

 ing to Heer (Fl. Tert. Helv., Vol. II, p. 71, PL LXXXVII and LXXXVIII, 

 figs. 5-15), the nervation is more sparse, the angle of divergence of all the 

 nerves greater, the number of lateral branches of the midrib less, and the 

 number of marginal teeth considerably greater. Professor Heer says (Joe. 

 cit.) that in P. aceroides the middle lobe of the leaf has two to three denta- 

 tions on either side, while in P. Haydenii the mature leaf has eight to ten 

 teeth on each side of the middle lobe. The difference before specified in 

 the form of the marginal teeth is very marked and strikes the eye at a 

 glance. In P. aceroides they are few, long, and acute, sometimes even 

 uncinate, while in P. Haydenii they are more numerous, less prominent, and 

 always obtuse, sometimes merely giving a wavy outline to the margin of 

 the leaf. 



Detached seeds are all that we have of the fruit, and these, though 

 plainly derived from a Platanus, in their condition of fossilization afford no 

 good characters with which to compare this species with the two now living 

 on this continent, or with the living and fossil species of the Old World. 



P. aceroides, according to Heer, had fruit in racemes like the Mexican 

 plane tree, while the fruit of P. occidentalis is single. In general aspect 

 the species now before us is more like the eastern than the western of our 



