In an article on “The late Extinct Floras of North America,” which appeared in Vol. ix of the Annals of the New York Lyceum of Natural History, in April, 1868, Professor Newberry describes certain fossil specimens of ferns occurring in Miocene argillaceous limestone at Fort Union, Dacotah, and refers them with little hesitation to this species. I have not seen the specimens, but, as similar venation and not very dissimilar fronds are seen in Woodwardia and Pteris, one may perhaps doubt the absolute certainty of the identification.
[1]Milde indicates several other unimportant variations; and Hooker & Baker have as varieties of this species the East Indian _Aspidium cochleatum_, and _Aspidium elongatum_, from Madeira and the Canary Islands. The latter they give as occurring also in the southern United States, evidently supposing it to be the long-lost _A. Ludovicianum_ of Kunze. For abundant synonymy of _Aspidium Filix-mas_ the student is referred especially to the works of Hooker, Milde, Mettenius and Moore, as quoted above.
[2]See the “Flora of New York” for some figures of laciniated and forking fronds.
[3]Prof. Amos Eaton, grandfather of the present writer. Eaton’s “Manual of Botany” went through eight editions from 1817 to 1841.
[4]I find one or two instances of a slight enlargement of the apex, as if there were an attempt to form a proliferous bud.
[5]“In _O. sensibilis_ the sori are borne on the middle of the vein, and consist of a tough cylindrical receptacle, three or four diameters in height, bearing sporangia thickly all over its surface, and covered when young by a delicate hood-like indusium, attached half-way or more around the base of the receptacle on the inferior side, and having the crenulate-margined opening toward the apex of the segment. At an early stage the blackberry-shaped sorus is almost entirely covered by the indusium, which resembles a closely drawn cowl, but with the growth of the sporangia it is thrown back, or rent, and soon disappears, the sori becoming confluent. The receptacle is very persistent, and may be seen, covered with the stalks of the sporangia, in the dried last-year’s fertile fronds, which are always found where the plant grows.”