322 MESOZOIC FLORAS OF UNITED STATES. 



ends and the other begins." Nevertheless . we have every reason to 

 beUeve that at the one end of the series there are characteristic ferns 

 analogous to such living forms as Oleandra and Acrostichum, as well as 

 marattiaceous forms, and at the other an important list of cycadaceous 

 forms. The closely related genera Pterophyllum and Anomozamites 

 may be cited in this connection. Anomozamites minor (Brongn.) Nath., 

 as restored by Nathorst from specimens from the Rhetic of Scania, with 

 its Williamsonia-like fructifications, Xilsonia-like foliage, and branching 

 habit, is especially to be mentioned in this connection as one of the most 

 interesting fossil plants known.'' This series is at the same time an 

 exceedingly important one, covering as it does a period extending over 

 much of the Paleozoic to the close of the Jurassic at least, a period so 

 fertile in the evolution of higher forms. 



Nilsonia nigracoUensis occurs between the Jurassic beds 3'ielding 

 the genus Cycadella of Ward and that higher up from which he has 

 described so many Cycadeoideas. This gives it as a probably allied 

 plant much additional interest. 



Perhaps next in interest to the sections already given is that at the 

 so-called "Calico Canyon," near Buffalo Gap, South Dakota, so named 

 from the beautifully banded sandstone there quarried. This section is 

 as follows: 



Rim section on the northern slope of Calico Canyon near Buffalo Gap, South BaTcota, beginning in the banded 

 sandstone quarry, and extending from the marine Jurassic to the Fort Benton. 



Feet. 

 34. Fort Benton shales. 



33. Light-colored sandstone 10 



32. Various shaly or sandy layers -10 



31. Heavy and prominent bed of flesh-colored sand rock capping the escarpment and containing some 



silicified wood 50 



• « In this connection the following remark of Nathorst (op. cit., p. 42) is of interest: 

 " Nilsonia polymorpha Schenk is considered by Saporta, as well as by Schimper, to be so closely related 

 to N. brevis and N. elongata of Brongniart that both the latter species may perhaps be only varieties of it. 

 A specimen from the gray shales of Palsjo (Swedish Rhetic) may at first sight give sohie support to this view. 

 Such as have entire margins have a habitual Tseniopteris form. For this reason Count Saporta verbally 

 suggested the idea that A', polymorpha possibly included a Taeniopteris. The Palsjii specimens with well- 

 preserved margins show, however, that this is not the case, a fact which Saporta later admitted in writing. 

 The nervature as above described is characteristic of Nilsonia, with simple lateral nerves, while these nerves 

 in Tsmiopteris are dichotomously branched at the base. Nevertheless, there occur, as stated, transitions 

 from the one form to the others." 



I need only remark that as we can not rely on form, and as we now know we can not separate these genera 

 on the basis of dichotomy of the lateral veins, there is, in the absence of a knowledge of their fructification, no 

 very positive means of separation. 



t Nathorst, Nya Anmarkningar om Williamsonia: (_)fv. Kongl. Svensk. Vet.-Akad. Fi'irh., pp. 359-365. 

 Stockholm, 1888. 



