Bryales. 35 
absence of a basal membrane to which the teeth may be joined 
below, etc. (i.) Arcliidioidecz, with the single genus Archidium. (ii.) 
Dicranoidecc. Teeth usually cleft into two or rarely three lobes, 
outer layer with longitudinal striations and thinner than the inner 
layer, which has more or less distinct transverse bars, no basal 
membrane, no properistome. Families :—Dicranaceae, Fissiden- 
taceae, Leucobryaceae. (iii.) Monocranoidece. Teeth undivided, 
outer layer with papillae, the two layers of about equal thickness, no 
basal membrane, properistome often present. Families :—Leuco- 
phanaceae, Syrrhopodontaceae, Calymperaceae. (iv.) Ditrichocra- 
noidece. Teeth usually divided deeply into two or rarely three 
filamentous lobes, usually with papillae, transverse bars feebly 
developed, basal membrane usually present, no properistome. 
Families:—Trematodontaceae, Angstrcemiaceae, Ditrichaceae, Tri- 
chostomaceae. (v.) Platycmuoidece. Teeth broad and thin, un¬ 
divided or perforated by slits—more rarely split into two or three 
lobes, outer teeth thicker than inner, no basal membrane, properi¬ 
stome sometimes present. Families:—Seligeraceae, Grimmiaceae, 
(B) . Hetevolepidece. In the single small family placed here 
(Encalyptaceae) the calyptra differs from that of other Bryales by 
its relatively large size and long-continued growth and persistence 
—it only becomes detached when the operculum falls off, coming 
away along with it. In the single genus Eucalypta, along with 
great uniformity in all other characters, there is great diversity in 
the structure of the peristome, which may be constructed either on 
the Haplolepidean or the Diplolepidean plan, and in the latter 
case the superposed exostome and endostome are sometimes 
coherent, owing to incomplete resorption of the horizontal walls of 
the peristome-forming cells. According to Philibert, Eucalypta 
represents the synthetic ancestral type from which the Haplo- 
lepideae and the Diplolepideae have arisen. 
(C) . Diplolepidecc. In this group there are very few cleisto- 
carpous forms, as compared with the Haplolepideae, and to it 
belong the great majority of the Bryales, including practically all 
the pleurocarpous forms and some of the largest of the acrocarpous 
families. The peristome is double, very rarely apparently single 
or chambered ( Splachnum , etc.) and still more rarely absent alto¬ 
gether. The exostome consists of sixteen teeth, sometimes joined 
in pairs, occasionally perforated or split; the outer layer consists 
of two series of membranes, the inner of a single series. The 
