JIKASSIC I LOKA OK I)()l(;LAS COrNTV. ORE(;. 103 



mon form the leaHot maintains its width to the end, wtiere it is rounded 

 off with a seinicii-cuhir curve. They are sometimes truncate. In tlie 

 rarer eases the tip is nai'rowed hy heinsr i-oumled off ol)H(iuely on its pos- 

 terioi' tei'iiiina! marj;in. The average leaflets from tlH> mi(ldl(> portion of 

 the leaves may he taken as having a length of IS mm. and a width of 

 .5 mm. Those of maximum size from the same part of the leaf may attain 

 a length of 20 nun. and a width of 8 mm. The smallest leaflets from 

 similai' parts are lo mm. long and 4 nun. wide. The nerves are very fine 

 and raiely visil)le. They can he seen distinctly only with the lielp of a 

 lens. Tlu>y are attached at a right angle to the axis, are parallel to one 

 another, and not forked. They vary somewhat in number according to 

 the width of the leaf, .\bout 15 may be taken as the average, l)ut 17 or 

 more may occur. They do not vary in strength from one end to the 

 other. Most of the forms given l)y Oldham and Morris fi'om the Indian 

 Rajmahal series are larger than the average forms from Oregon, but the 

 Rajmahal Pterophylla generally show a remarkable robustness. 



This plant was found in the Oroville flora" in a few specimens forming 

 an important connecting link between that and the Oregon Jurassic. 

 Heer describes from the Jurassic of Siberia a fossil that he names Ptero- 

 lilniUiun Sensinovinnnni.'' This seems to be the same as the plant now 

 in (juestion. He separates it from P. rajmahalense because it has fewer 

 nerves, but he says the nerves are obsolete, and, as he had in hand only 

 one small fragment, it is not probable that he saw all the nerves. In the 

 hundreds of specimens fountl in Oregon only a few show the nerves 

 distinctly enough to count them. 



PI. XXI, Fig. 1, shows the lower portion 'of a leaf with leaflets of 

 medium size. Fig. 2 is an enlarged portion of Fig. 1. Fig. 3 gives a 

 similar part of another leaf, with short, wide leaflets, the lowest ones 

 abnormally wide, and also a portion of the petiole. Fig. 4 gives the ter- 

 minal part of one of the smallest leaves, showing the two end leaflets 

 abruptly much reduced in size. These are enlarged in I'ig. 5. Fig. 6 

 gives the basal part of a leaf carrying leaflets of the greatest width, and 

 showing an abnormal widening of the liasal ones. Fig. 7 shows nearly 

 an entire leaf with leaflets of the largest size. 



aTwentieth Aim. Kep. U. S. Geol. Surv.. I't. II. 1900. j). 3o4, pi. Ivi, figs. 4, .5. 

 ''Fl. Foss. Arct., Vol. IV, Pt. II, p. 10.5, pi. .\.\iv, fig. S. 



