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and open irregularly by imperfect valves or by a portion of the top coming 
off after the manner of a lid. In this family the capsules and usually the 
antheridia are borne on special long-stalked receptacles well illustrated by 
the familiar Marchantia. 
Key to the Genera. 
i. Sterile stems bearing abundant gemmse in shallow open receptacles. . . .2 
Sterile stems without gemmse 3 
2 Found only in and around greenhouses; gemmse in crescent-shaped 
receptacles; never fruiting in our region Lunularia. 
Growing abundantly everywhere; gemmse in cup-shaped receptacles: cap- 
sule-bearing receptacle with 7-1 1 conspicuous rays Marchantia. 
3. Thallus large ; 2-6 inches long and ]/ z inch or more wide, distinctly areo- 
late as in Marchantia, but areolse larger and hexagonal. . . Conocephalus. 
Thallus less than two inches in length and much narrower 4 
4. Pores (stomata) scarcely distinguishable; antheridia in sessile receptacles 
which might be mistaken for gemmse; thallus purple on the margins; 
midrib strong underneath but not conspicuous above. ....... Reboulia. 
Pores conspicuous, white: antheridia in peduncled disk-like receptacle; thal- 
lus with numerous dark purple scales underneath Preissia. 
Pores conspicuous; antheridia immersed in the thallus; thallus purple 
underneath, at least along the margins 5 
5. Perianth conspicuous, split into 8-16 fringe-like lobes; peduncle not 
chaffy Asterella. 
Perianth lacking: peduncle chaffy at top and bottom Grimaldia. 
(The Reboulia of this key is the Asterella of Gray’s Manual and the 
Asterella is the Fimbriaria of that work. ) 
THE THALLOID SCALE MOSSES (METZGERIACE/E). 
The spore bearing portion of plants of this family is like that of the 
Scale Mosses, but the green part of the plant is a thallus instead of a leafy 
stem in nearly all cases. There are, however, some intermediate forms in 
the family in which the thallus is divided into leaflike lobes. The thallus is 
much less highly differentiated than in the Liverworts and Riccias: there 
are no areolse or pores (stomata), and the thallus is much thinner than in the 
Liverworts, in some species consisting of only a single layer of cells except 
at the midrib. The capsules are borne singly on setae arising directly from 
the thallus. They are spherical to elongated-ovoid and remain enclosed in 
the calyptra until mature when the setae rapidly elongate and break open the 
calyptra which is left at the base of the seta. The capsules open by four 
valves as in many of the Scale Mosses. A careful search of wet bare earth 
in shaded or springy places will nearly always yield one or more species of 
this family. 
Key to the Genera. 
1. Thallus with a distinct midrib 2. 
Thallus without a distinct midrib 4- 
2. Thallus 1/25 to 1/12 inch wide, dichotomously branched, cilliate along 
the margins Metzgeria. 
