344 ON LYELLIA, LEPTOSTOMUM,
Thus Gymnostomum microstomum, the Hymenostomum of the present paper, has less the habit of the genus in which it is placed than of Weissia, to some of whose species, especially W. qffinis and tric/wdes, it seems. to approach even in the structure of its peristomium.
Several species of that section of Gymnostomum, to which perhaps the genus should be limited, especially G.fascicu- lare, Bonplandii, and Bottleri, can hardly be distinguished from Weissia Templetoni}
575] Gymnostomum or Jnictanyium pulvinatum agrees in every other part of its structure with Grimmia.
Gymnostomum lapponicum, notwithstanding the difference of calyptra, may be considered as related to Grimmia Baviesii, and consequently to Orthotrichum, which G. Baviesii 2 resembles in its teeth being approximated in pairs.
Gymnostomum viridissimum has exactly the habit and calyptra of Zygodon.
Gymnostomum pennatum (Schistostega of Mohr,) in one remarkable character may be compared with Fissidens?
1 Weissia Templetoni, along with a nearly related species found in New Holland, Funaria minor of Delile (Flor. jFgypt.), and perhaps also (Veissia radians, may form a genus distinct from Weissia, and nearly related to Funaria, differing chiefly in the irregular bursting and evanescence of the inner peristo- mium, which in Funaria is regularly divided and generally persistent, though in some cases perhaps equally deciduous. In a variety of Weissia Templetoni, or a very nearly related species, collected in 1800 in the county of Donegal, I have observed the outer peristomium to be not unfrequently wanting, even before the separation of the operculum ; a fact which, if hereafter confirmed, would establish its affinity to Gymnostomum fasciculare.
2 Griffithia Baviesii nob.
3 As Schkuhr (in Krypt. Gewach. ii, p. 31, t. 12) has ascertained that the operculum of Gymnostomum pennatum separates entire, the genus Schistostega must be again reduced to Gymnostomum, until other distinguishing characters are discovered.
Its resemblance to Fissidens consists in the somewhat similar disposition of leaves.
In Fissidens, as limited by Bridel, {Muscol. Nov. p. 186) the leaves are uni- versally described as presenting their margin instead of their disk to the stem, and as having a doubling of the lower half of their inner or upper margin, ex- tending as far as the nerve.
On this view Bridel (inl.cit.) has formed a separate section of the order, consisting of Fissidens and Octodiceras ; and hence also M. de la Pylaie has changed the name of Fissidens to Skitophyllum. {Journal de Botan. Appliq. iv, p. 133.) It seems to me a much simpler explanation of the apparent anomaly to consider the supposed doubling or division of the leaf as its true disk, and
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