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The indusium is white, semi-transparent and entire. The plant is 
one of unusual elegance, both on account of its minute subdivision, 
and its smooth shining surface. 
No one who has observed the venation in this plant, and is 
acquainted with our British Asplenieœ, can fail to notice the simi- 
larity in form and division and in the condition of the veins, that 
exists between some of its ultimate pinnules, especially the shorter 
and broader ones of the less divided fronds, and some of the fronds 
of Asplenium septentrionale; there is no definite midvein in either, 
but a series of furcations only. This plant alone furnishes sufficient 
evidence against the adoption of the Amesium or Acropteris group as 
a genus. 
This acute variety differs from the normal form of Adiantum- 
nigrum in its more subdivided fronds, in which the deltoid form is 
usually strongly developed, in its thinner, harsher, and more papery 
texture, and in the presence throughout of linear acute erect segments 
and teeth. As to its distinctness, our enumeration of the varieties or 
forms occurring in Great Britain will show that in composition it is 
simulated by decompositum ; in texture by oxyphyllum especially, and 
by intermedium in a considerable degree; and in the presence of linear 
segments or teeth, both by oxyphyllum, in which the teeth though _ 
sharp are short, and by fissum and acutidentatum, in which the nar- 
row marginal divisions are, perhaps, rather monstrous developments 
of the teeth, than normally narrow divisions of the pinnules. "These 
points of resemblance, however, and the occurrence of other foreign 
intermediate states, have determined us in retaining acutum as a 
variety of Asplenium Adiantum-nigrum. We have only seen true 
examples of this variety from Ireland, in which the following habitats 
are recorded :—Kerry : Turk Waterfall Killarney, Dr. Mackay, 
Dr. Allchin, and others ; foot of Cromaglaun near the lower end of 
the upper lake, G. Maw; above Blackstones, Glouin Caragh, Inve- 
ragh, G. Maw; Cahir Conree, a mountain near Tralee, W. Andrews. 
Dublin: Dublin mountains, 1854, D. Orr. Cork: near Garry- 
eloyne, Blarney, 1857, Miss Townsend. Mr. C. Johnson, in 
Sowerby's Ferns of Great Britain, states that in 1891, he gathered 
a plant undistinguishable from this, on the walls of the Cathe- 
dral of St. Asaph in Wales; it has further been reported from 

