320 MESOZOIC FLORAS OF UNITED STATES. 



The type specimen was collected near the summit of the Black 

 Hills rim, 5 miles north of Sturgis, S. Dak., and has been presented to 

 the Yale Museum. It consists of a small slab of fine-grained drab sand- 

 stone containing numerous imprints of portions of fronds or pinnules, 

 with some fragmentary, but distinct, specimens of Thyrsopteris dentifolia 

 Font.," PI. LXXIII, Fig. 15d, and was obtained in situ from the base of 

 the first sandstone stratum which here overlies the Beulah shale, containing 

 Jurassic dinosaurs. The horizon of the present new Nilsonia therefore 

 belongs at the very base of the Lakota formation of Darton. 



In considering the relationships of the present species I will explain 

 that I at first referred it to the genus Tseniopteris of Brongniart, but on 

 the reference of my manuscript by Professor Ward to Professor Fontaine 

 the latter replied that he considered it a Nilsonia. This reply Professor 

 Ward was so kind as to send me, and as it deals with the distinction 

 between these very important genera, as well as with the only known 

 American species of Nilsonia with which the Black Hills specimens may 

 be directly compared, I give it in full. Professor Fontaine says: 



The supposed "Tseniopteris" of Mr. Wieland is an interesting plant. His fig- 

 ures and description indicate that it is a Nilsonia rather than a Taniopteris. It 

 seems that we can not insist on segmentation of the lamina of the leaf as a diagnostic 

 character of Nilsonia, although the laminse are generally segmented. This would 

 leave as the only important difference between the two genera the fact that in Nil- 

 sonia the lamina of the leaf is attached to the upper surface of the midnerve, while 

 in Tseniopteris it is attached to the sides. Hence in Nilsonia, on the upper surface 

 of the leaf, the bases of the lateral nerves are inserted on a raised line or cord, running 

 about the middle of the midnerve, which latter is inconspicuous. In Tseniopteris 

 the lateral nerves are inserted on the sides of the midnerve, which is conspicuous. 

 These Nilsonia features are very evident in Mr. Wieland 's plant. This plant is strik- 

 ingly like Nilsonia parvula (Heer) Font, of the Jurassic of Oregon. As, however, 

 it is constantly larger and more robust than the predominant forms of that fossil, it 

 is probably specifically different. It looks much like a modified descendant of N. 

 parvula, the larger forms of which are fully as large as the smaller ones of N. nigra- 

 collensis. Heer made N. parvula a Tseniopteris, but the numerous Oregon forms 

 show that it is a Nilsonia. As this plant was exceedinglj- abundant in the Oregon 



a Described in Ward's Cretaceous Formation of the Black Hills (Nineteenth Ann. Rep. U. S. Geol. Surv. 

 Pt. II, 1899, p. 660, pi. clxvi, figs. 6-9), from the Haj- Creek region, W.voming, as. coming from "over coal 50 

 feet above the Jurassic." The main Aladdin Wyoming coal seam lies immediately over the shale numbered 3 

 in rav section taken north of Piedmont, and hence in the same relative position. 



