"^"I'saa" 1 PKOCKEi)IN(;s oK 'I'llH NATIONAL MUSEUM. 2G5 



Dioonites Buchianus, v;ir. angustifolius Font 



I'l. xx.wi, Fijf. (i. 



In the Potomac strata of Virginia a Dioonites was found witli leaflets 

 mncli narrower than the normal form. As it did not {graduate into the 

 normal />. BuchiauuH, and apparently was not an accidentally narrowed 

 form of that species, the writer in Mono<4r;i])h xv of tiie ])ublications of 

 the U. S. (leoh)j^ieal Survey, J 'art i, text, p. 185, proposed to consider 

 it a variety. This narrow form is i)resent in the Texas region, as is shown 

 in one well characterized siKM;imeii. This specimen shows leaflets 

 exactly like those of the Virginia J'otomac. 



Dioonites Dunkerianus ((Jii]))*.) Mi<iiiel. 

 ri. xxwi. I'ix- 11'; I'l. xxxvii, Fig. 1. 



Leaves large; midrib very strong; leaflets spreading, closely placed, 

 somewhat thickened at base, slightly and gradually narrowed toward 

 their bases; attached to the sides of the niidiib, as in I). Buchianus, 

 with a slightly protracted and decurrent ba.se, luirrowly linear in shai)e, 

 obtuse to subacute at the tips, very thick and leathery in substance, 

 with a lirni durnbh^ ('])iderniis, jittiiining appaiently maximum length 

 of 15 ccnitimeters and a width of "J to '.i millimeters; nerves obscure, 

 api)arently live to six in number, very slender, and immersed in the 

 thi<;k leafsubstauee. 



Several fairly well preserved specimens of this noteworthy plant were 

 obtained. They apparently belong to tlie middle and upper portions 

 of the leaf, and the basal aud t(!rminal jtortions wer<i not seen. The 

 S[»ecimens are .somewhat distorted, so that the angle made by the leaf- 

 lets with the midrib can not certainly be made out. They seem to go 

 ofl" at an angle of about 45 degrees. 



This plant agrees so well with I). DunJcerianus (Gopp.) Miquel, from 

 the Wealden of Hanover, that it can not l)e separated from it. It clearly 

 belongs to the same genus with J>. Jiuchianus, wherever that may be 

 ])laced, but is decidedly distinct from it. S<;henk, in describing* I>. 

 J)unleriann.s; gives the length of the leaflets as 4 to ih centimeters. 

 I do not understand how he obtained these dimensions, for on PI. xv, 

 Pig. 1, of the same work he gives a figure of this plant which shows 

 leaflets 7 centimeters long with the entire length not preserved. That 

 they were considerably longer is shown by the fact that a leaflet 7cen 

 timeters long, with the end broken oft', shows no diminution in width. 

 S<;henk's figure rei>resenis the leaflets as they are shown in the Texas 

 plant. Pig, 1, PI. XXXVII of this paper, gives a portion of a large leaf 

 with the leaflets ol" only one side preserved. All of the width of the 

 mi<lrib is not preserved, ])ut its great size is indi<rate(l in the si)ecimen. 

 PI. XXXVI, Fig. 1-5, gives a specimen with a smaller midrib, showing its 



" Die Fossile Flora der Nordwestdeutsclieu Wcaldeu loriuation," pp. 30, 31. 



