36 THE LATER EXTINCT FLORAS OF NORTH AMERICA. 



separated from those of the known species of Juglans than are those of the 

 Pecan, and there seems little doubt that the tree, if now living, would fall 

 within the limits of Carya. 



In some specimens the lateral nerves are remarkably straight and 

 numerous, giving to the leaf very much the aspect of those of iEsculus; 

 but, from a comparison of the many leaves of this plant in the collection of 

 Dr. Hayden, I infer that they were not palmately grouped, but pinnate, the 

 form of the bases of the leaves indicating this. 



The tertiary nervation is also quite different from that of iEsculus. 

 In the latter genus it usually forms an exceedingly fine network filling the 

 interspaces between the secondary nerves, in which the straight transverse 

 latticelike bars so characteristic of the fossils before us are wanting. At 

 least this is the case with our American "Buckeyes." In 2E. Hippocastanum 

 of the Old World something of the kind is visible, but in prevalence and 

 regularity very unlike that in the fossil. 



In has been questioned whether these leaves should be referred to 

 Juglans or Carya, and after somewhat extensive comparisons I was led 

 to include them in the latter genus. In looking over the descriptions that 

 have been given of various fossil species of Juglans we find that quite a 

 large number of them should be rather reckoned as pertaining to Carya, 

 taking the fruit as a criterion. For example, in the J. corrugata of Ludwig 

 (Pakeontogr., Vol. VIII, p. 178, PL LXX) the form and the nervation of 

 the leaf is very much like this before us, only the nervation is a little less 

 regular and the marginal serration is coarser. The fruit associated with 

 these leaves is more nearly allied to that of our J. nigra than it is to the 

 fruit of the common species of Carya, whereas in the illustrations of J. levi- 

 gata, Brong, given by Ludwig (Pakeontogr., Vol. VIII, p. 134, PI. LIV, 

 fio-s. 1-6), we have leaves which correspond in a general way with these, 

 as far as form and marginal serration are concerned; nervation exceedingly 

 regular, but more camptodrome, and the fruit distinctly that of Carya. It 

 will be necessary to wait the discovery of the fruits which were connected 

 with these strongly marked leaves, an event which will be likely to occur 

 at no distant date, before deciding to which subdivision of the old genus 

 Juglans it belongs. 



Formation and locality: Tertiary (Eocene!). Mouth of Yellowstone 

 River, Montana. 



