348 ON LYELLIA, LEPTOSTOMUM,
579] By these lines also S. squarrosum is readily distin- guished from Octoblepharum, in which the apparent number of teeth is the same : for in Octoblepharum each tooth has only a single pellucid line ; and hence its affinity to certain species at present referable to Weissia, with a nearly similar habit and sixteen distinct teeth, whose axis is not perceptibly pellucid.
Weissia splachnoides differs from the other Splachnea in having sixteen equidistant teeth ; but as these teeth, accord- ing to the indication of the pellucid axis, are double, the arrangement may be compared with that of Tayloria and Systylium, in which the separation into thirty-two is com- plete, and the sixteen pairs equidistant. It agrees, however, also in this respect with Grimmia and with several species of Weissia : bnt in other important characters, as well as in habit, it is evidently related to Splachnum, and offers perhaps one of the best examples of the importance of the male flowers in distinguishing natural genera.
Even Tetraphis pellucida may be cited in proof of the same prevailing number in the peristomium ; each of its four teeth, when highly magnified, appearing to have seven longitudinal strias, which, according to this test, would make the real number thirty-two ; a structure contributing to fix the place of Tetraphis in the natural series between Splach- num and Orthotrichum.
580] Better evidence on the same subject is afforded by Trichostomum , Didymodon, and Leucodon,m all of which the thirty-two teeth are distinct, though approximated in pairs ; by the sixteen bifid teeth of Dicranum and Fissidens ; and by the like number of teeth with a perforated axis in Tre- matodon, Weissia nuda, Didymodon latifolium, and several species of Grimmia.
mosses differ materially even in this part of their structure ; and as other differences, of at least equal importance, also exist, both in the peristomium and male flowers, Octoblepharum serratum, whose habit is nearly that of Splach- num, may be distinguished both from that genus and from Octoblepharum^ the following characters.
Okthodon.
Fl. Fem. terminalis.
Peristomium simplex, octodentatum, dente singulo striis tribus iongitudinali- bus instructo (ideoque e quatuor coalitis composite).
Calyptra mitriformis (4-fida, pilosa).
FL Mas. terminalis, discoidcus.
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