50 Illinois State Laljoratorij of Xatunil Historij. 



{ Midrib wanting or not apparent C 



I Midrib clearly apparent D 



Sporogonium dorsal; elaters bispiral, free. II. Pellia. 



Sporogoniura borne on under side of thallus near the 

 margin; elaters unispiral, adherent to the apex of 

 the valves. I. Aneura. 



Inner involucre tulnilar, at first terminal, at length 

 dorsal; thallus sinuate or lobed. IV. Steetzia. 



Inner involucre wanting or early vanishing E 



Outer involucre wanting; fructification apical; thallus 

 simple or bifid. III. Blasia. 



Outer involucre monophyllous, ventricose; sporogonium 

 arising from lower surface of midrib; thallus fur- 

 cate. V. Metzgeria. 



r Leaves incubous: i. e. the apex lying on the base of the 



I next one above Gr 



F \ 



Leaves succubous: i.e. the apex lying under the base of 



1^ the next one above 



f Leaves bilobed or with a small ventral lobe at base . . H 



^ "] Leaves without ventral lolje at base, mostly 3-5-tootlied, 

 [ lobed or parted L 



f Amphigastria present* I 



H ^ Amphigastria wanting; lower lobe usually convex un- 

 1^ derneath. XL Radula. 



r Amphigastria entire or 2-toothed K 



1^1 Amphigastria 4-5-lobed; lobes of leaves divided. XIII. 

 1^ Blepharozia. 



•■■ Amnliiii'nstria firo obsolete or wanting in three species of Lejennia- 



