FLORA OF LAKOTA OF BLACK HILLS. 319 



Just east of Spearfish, S. Dak., there is such a locahty requiring further 

 examination, and on the outer rim, 16 miles north of the present section," 

 I secured fine specimens of a Nilsonia, which is a new species. It may be 

 characterized as follows: 



Genus NILSONIA Brongniart. 



Nilsonia nigracollensis Wieland n. sp. 



PI. LXXIII, Fig. 15a-d. 



While none of the fronds of the type specimen are complete, the parts 

 present are numerous, and include bases, middle portions, and tips, show- 

 ing both upper and lower surfaces, the venation of all being distinct. 

 From these various portions we may conclude that the entire blades were 

 probably 25 cm. in length. But they may perhaps have reached a length 

 of 30 cm., and, as in the case of all characteristic Nilsonias, there is evidence 

 of considerable variation in size. " As the base is long and tapering, the tip 

 blunt, and the greatest width not more than 11 mm., the fronds were 

 gracefully linear. Apparently, they were widest somewhere beyond their 

 middle point. By placing the base a, the middle portion h, and the tip c, as 

 shown in the figure, end to end, the general outline of a nearly complete 

 frond (or pinnule) will be obtained. 



As indicated in the figure, the midrib is distinct, but not heavy. The 

 lateral nerves are normally simple and parallel, but very rarely they fork 

 close to their origin. They rise only slightly just at their origin on the 

 slender raised line marking the upper surface of the midrib, but more 

 sharply at their tips, their general course lying quite uniformly at an 

 angle of about 75° to the midrib. Both their direction and distance apart 

 are quite constant from base to tip. There are from 23 to 26 lateral veins 

 to the centimeter. 



Locality and horizon. — Thls Very characteristlc new species receives its 

 name from the Black Hills, being the first example of the Nilsonia- 

 Tseniopteris form of frond to be reported from this region. 



« Both these plant localities lie at the base of Barton's Lakota sandstone. 



b This is one kind of evidence in favor of the once pinnate character of many of the species of this and the 

 related genera, which is not to be neglected; the differences in size as a varietal character, in the case of speci- 

 mens from the same locality, is hence of doubtful value. Thus in Nilsonia polymorpha Schenk it seems to me 

 -the best explanation is that the multiform blades are the pinna; of, not a bipinnate, but rather a bipinnoid 

 frond of triangular outline. 



