82 i^'LUliA OF LOWEK GOAL MEASUEES OF MISSUUlil. 



on the upper surface, are always clear on the lower surface, where the^^' are 

 like fine wires, sometimes appearing double, as in a poi'tion of the specimen 

 from which the detail, PI. XXXVI, Fig la, is drawn. 



The specimens which I have described under the above name belong 

 to the complex of Pecopteris species, among which Pecopteris oreopteridia 

 (Schloth) Brongn. and P. lepidorachis Brongn. are the most familiar. In 

 fact, I was at first disposed to identify them as the latter species, for, while 

 apparently distinct from the unequivocal type ^ figured by Brongniai-t, in 

 which the pinnules are narrower, the upper division of the nervils in the 

 larger pinnules in most cases forking again, the fragments from Missouri 

 present a general aspect, form, and .arrangement of the pinnas and pinnules 

 so strikingly like those of the specimens illustrated by Zeiller ^ or Potonid ^ as 

 to argue strong'ly, especially in the presence of a similar system of ner\'a- 

 tion, in favor of their specific identity. But a more minute comparison 

 seems to show in the American plant a tendency to greater decurrence in 

 the midribs and sinuses; the pinnules, which appear slightly broader in 

 proportion to their length, often contracted on the upper side at the base; 

 nervation distinctly constricted on tlie lower side also; the midrib rather 

 stronger, and the nervils slightly closer and usually more oblique. In 

 respect to the decurrence of the midrib, the form of the smaller pinnules, 

 the contraction of the larger pinnules, and the nervation, our plant is some- 

 what intermediate between P. lepidorachis and P. oreopteridia. In the latter, 

 however, the upper nervil is more apt to fork again, even in the smaller 

 pinnules, while the rachis is always smooth. Still, the resemblance to that 

 species as generally figured is very strong. Pecopteris Jenneyi * has much 

 in common also with P. densifolia Goepp. and P. Dcmhreei Zeill.,^ but in the 

 former the pinnules are apparently even more constricted at the base, and, 



' Hist. vi?g. foss., p. 313, pi. ciii, fig. 1. Figure 5 of the .same plate is also referred to this species 

 by Brongniart in the text of P. lepidorachis, but it is also similarly assigned on the opposite page 

 (ZVi) %o P. xilalyrachls, with ■which reference the explanation of the pi. ciii agrees. M. Zeiller (Fl. 

 foss. houill. Comraeutry, vol. i, p. 127) is disposed, on account of the coarsely punctate rachis, to con- 

 sider it as perhaps one of the types of P. lepidorachis, although the nervils are delineated as simple. 

 Lesquereux, however, copied this figure in pi. xli of the Coal Flora (figs. 5, 5a) and gives it as the 

 illustration of P. plRtijrachis, a species described as having a smooth rachis. 



- Fl. foss. houill. Commeutry, pi. xiii, fig. 5 ; pi. siv, iigs. 1-3. 



•■' Fl. Rothl. Thiiringen, p. 72, pi. v, figs. 2, 2(). 



^The small pinnules of /-". Jenneyi are usually rather wider proportionately, with more oblique 

 nervation than in the latter species, as illustrated by Potonie, Fl. Rothl. von Thiiringeu, pi. vii, figs, 

 la, 16, p. 68. 



'' Fl. foss. houill. Communtry, jit. 1, p. 147, pi. xv, figs. 1-5. 



