FLORA OF LAKOTA OF I'.FACK IIIFLS. 319 



Just east of Bpearfish, S. Dak., tliore is sucli a locality rfHiuiring furllicr 

 rxaiuiiialioii, and on the outer rim. Ki miles north of the [)resent section," 

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

 characlei'ized as follows: 



(ionus NILSONTA Bronmiiart. 



NiLSOXIA NKJRACOM.KNSIS \\'i('l;Uul II. S]). 

 PI, LXXIIl, Fi--. l.Kl (i. 



A\'hile none of the fronds of the type specimen ar(> complete, the i)arts 

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

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

 I'^rom these various portions we may conclude that the entire blades were 

 probably 2.5 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 

 gracefulh" linear. Aj^parently, they were widest somewhere beyond their 

 middle point. By placing the base a, the middle portion 6, 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 cjuite constant from base to tip. There are from 23 to 2() lateral veins 

 to the centimeter. 



Locality and horizon. — Thls vcry characterlst ic new species receives its 

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

 T*uiopteris form of frond to be reported from this region. 



" Botli tlicse pUuit lociililics lie at tlie Ijase of Darton's Laliota sandstoiif. 



''This is one kind of evidence in favor of tlie once pinnate eliaraoter of many of tlie species of tliis and tlie 

 related genera, wliicli is not to he neglected; the did'erences in size as a varietal character, in the case of speci- 

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

 the best explanation is that the nniltifurin blades arc the i)imi;e of, not a bipinnatc, but rather a bijiinnuid 

 frond of triangular outline. 



