46 THE FLOEA OF THE DAKOTA GROUP. 



In tlie TUimorous specimens of the leaves of Popnlites of the Dakota 

 Group, some of wliich may be referable to other generic divisions, there 

 is a more or less marked difference in the secondary nervation, which some- 

 times appears camjitodrome by the thinning of the nerves quite near the 

 borders, and sometimes is distinctly craspedodrome, the borders l^eing entire, 

 undulate or denticulate by the outside projection of the nerves. These form 

 a peculiar group, comprising PopulUes qjclophyllus Heer, P. litif/mus Heer 

 Lesq., P. elegnns Lesq., P. lancastrknsls Lesq., Populus f cordifoUa Newb., 

 and the Popnlites Sternbergii, now described. 



The leaves of this group, like those of some others of the Cretaceous, 

 seem to represent by gradual modifications intermediate forms, whose spe- 

 cific reference remains uncertain or difficult to fix. 



Habitat: Two and one-half miles south of Glascoe, Kansas. Nos. 422 

 and 426 of the Museum of Comparative Zoology of Cambridge, Massa- 

 chusetts. 



PopuLiTES LiTiGiosus (Heer) Lesq. 

 PI. VII, Fig. 7; PI. VIII, Fig. 5; PI. XLVI, Fig. 6; PI. XLVII, Fig. 1. 



Populus litigiosa Heer, Phyll. Cr6t. du N6br., p. 13, Pi. i. Fig. 2 ; Newberry, Illustr. 

 Oret. and Tert. PI., PI. iii. Fig. 6; PI. ii, Fig. 1 ; Schimper, Pal. V6g., vol. 2, p. 691. 



Leaves rounded, entire at the truncate or broadly cuneate base; lateral 

 nerves in four pairs, the basilar opposite, the upper alternate distant; ner- 

 villes curved, continuous or divided. 



Tlie species is really little known, though often quoted. The above de- 

 scription is that of Heer, made from a mere fragment of a single leaf, of which 

 the base and the median part only are preserved, the borders all around 

 and the upper part being destroyed. Fig. 5 of our PI. VIII agrees with what 

 is seen of the leaf represented by Heer, and with his description, except 

 that the number of the lateral nerves is greater, being six instead of four, 

 with still one pair of basilar veiulets following close to the borders, and an 

 intermediate nerve on one side included in the space between the base of 

 the lowest lateral nerves and that of the leaf. But this leaf is much larger 

 than that figured by Heer. The lateral nerves are all parallel, distant, 

 straight, thinning toward the borders, ramose and craspedodi-ome, as well as 

 their divisions, the borders being either entire or somewhat undulate. In Fig. 

 7, PI. VII, the lower lateral nerves are not opposite, and the space between 

 their point of attiichmont and the base of the leaf is much narrower. With 

 the smaller size of the leaf it is the only point of difference between this and 



