Chignik Area. Collected from the same section as USGS 11502 (Sutwick island D-3 Quad)
Lat. 56°55´52" N., Long. 157°57´11"W, but stratigraphically lower than USGS 11502, which is regarded as representing the Tolstoi Formation. It is likely that this specimen is from the Chignik Formation.
Fronds: radius stout, straight or slightly curved, rounded on underside, grooved on upper side; lamina dissected into pinnae; pinnae irregularly arranged, broad junction with rachis, parallel or tapering towards obtuse to rounded apex, pinnae margins entire, venation parallel, typically approximately 20 veins per centimeter.
Specimen USGS 11598.8 undoubtedly represents the same species as those specimens figured by Hollick (1930) under the name Nilssonia serotina. All his specimens assigned that name were collected from the Alaska Peninsula. Specimen USGS 11598.6 on the other hand is more like N. yukonensis Hollick from the lower Yukon River localities. N. serotina, however, also encompasses a wide range of morphologies, some of which, in places, lack the pinnatifid dissection of the frond. In the absence of cuticle characters the determination of species within the genus Nilssonia Brogniart is very unreliable.