NO. 1884 FOSSIL PLANTS — KNOWLTON 493 



sided, closely sessile or slightly decurrent, cut more or less deeply 

 into oblong, obtuse lobes — usually five on each side — which are 

 entire or occasionally with a few low teeth ; nervation delicate, con- 

 sisting of a slender, slightly flexuose pinnately dichotomous midvein, 

 with lateral nerves at an acute angle of divergence and once or twice 

 forked ; sori small, globular, on the apex of a free vein, and marginal 

 on the tips of the lobes of the pinnules, mostly on the upper side. 



This species is represented by a large number of specimens from 

 a number of widely separated localities, though so far as known 

 all are from the same geological horizon. They are mostly in the 

 form of portions of detached pinnje, of greater or less size, although 

 occasionally a pinna is found nearly perfect, and in a few instances 

 a considerable portion of the whole frond has been found, such, for 

 instance, as that shown in plate LXiv, figure 5. From this it appears 

 that it was a delicate fern of rather strict habit and apparently 

 lanceolate in general outline. It is impossible to give the exact size, 

 but it was at least 15 or 20 cm. in length and 8 cm. or more in width. 

 It is not rare to find pinnse that are 8-10 cm. in length, though the 

 majority are apparently somewhat less than this. They are alter- 

 nately and very obliquely placed on the rachis, and have a relatively 

 rather strong secondary rachis. The pinnules are also obliquely 

 attached, and are either sessile or sometimes slightly decurrent. In 

 shape they are deltoid or oblong, largest on the upper side, and cut 

 often rather deeply into oblong, obtuse usually entire lobes, on the 

 .apices of which, usually on the upper side, the sori are borne. The 

 largest pinnules observed are about 18 mm. in length and 10 mm. in 

 width, but the average size is much less. 



This fern is referred without hesitation to the genus Dennst?edtia, 

 since it is closely congeneric in habit, nervation, and fructification 

 with the numerous species now segregated under this designation. 

 It is not particularly close to Dcnnstccdtia puiictilobula, the only liv- 

 ing North American species, but appears to find its closest relation- 

 ship in D. scahra (Wall.) Moore, a species widely spread over China 

 and tropical Asia. From this it dififers in being bipinnate instead 

 of tripinnate, as well as in its narrower fronds, more slender pinnje. 

 and much smaller pinnules ; its general appearance, however, is much 

 the same. 



The fern here renamed Dennstcedtia americana has had a rather 

 complicated nomenclatorial history. It appears to have been first 

 found in 1875 "^ai" Porcupine Creek, vSaskatchewan, by the British 

 North American Boundary Commission, and was referred by Daw- 



