40 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Thallus usually larger, less closely at- 
tached. 
Spores commonly medium-sized and 
ellipsoid; thallus usually large and 
rather closely attached ............. 
Spores commonly smaller, short. or sub- 
spherical; thallus usually smaller 
and less closely attached........... 
Spores not simple. 
Spores 2-celled. 
Spores hyaline, the cells polar; thallus usually 
yellowish, varying toward gray........... 
Spores brown, the cells not polar. 
Thalloid exciple usually of the color of the 
thallus, usually sea-green or brownish. . 
Thalloid exciple blackening, thus becoming 
indistinet, except in sections; thallus 
S@a-PreeN 2... ...222 22.2 ee 
Spores muriform, brown or hyaline. 
Apothecia clustered on the large thallus. .... 
Apothecia not clustered, immersed in the mi- 
nute, not plainly foliose thallus.........- 
Algal cells nearly always blue green (Nostoc, Gloeo- 
capsa, Polycoccus, Dactylococcus, etc.). 
Algal symbiont Nostoc, showing the pseudocysts 
and heterocysts plainly; thallus becoming ge- 
latinous when wet. 
Thallus having a cortex of a single layer of cells. . 
Thallus without a cortex. 
Spores hyaline, several-celled, not muriform... 
Spores hyaline, more or less muriform at ma- 
turity. 2.2.22... ee 
Algal symbiont not Nostoc. 
Algal cells in groups (Gloeocapsa?) in the dark- 
colored thalli on rocks..................... 
Algal cells in chains, the chains not easily dis- 
cernible (Polycoccus or Dactylococcus, usu- 
ally) in the commonly large thalli. 
Thallus cellular throughout, closely adnate. .. 
Thallus not cellular throughout. 
Thallus having cyphelle or whitish spots on 
the lower side; spores 2 to 4-celled, hya- 
line or brown......-......22.2..2..... 
Thallus without cy phellse or whitish spots be- 
low. 
Thallus with cellular cortex above and 
below. 
Spores simple, minute, numerous in each 
ascus; thallus small............... 
Spores not minute, not numerous in each 
ascus. 
Spores simple, hyaline, ellipsoid; thal- 
lus small, of various colors. 
PARMELIA (p. 190). 
CETRARIA (p. 199). 
TELOSCHISTES (p. 217), 
Puyscia (p. 224). 
. PyXINE (p. 230). 
UMBILICARIA (|. 168). 
ENDOCARPON (p. 244). 
Leproaium (p. 139) 
SYNECHOBLASTUS (p, 133). 
CoLLEMA (p. 136). 
OMPHALARIA (p. 144), 
Heppta (p. 149). 
Sticta (p. 154). 
. Enpocarpiscum (p. 148). 
Some species of PANNaARIA (p. 150). 
