FINK—THE LICHENS OF MINNESOTA. 
Proper exciple absent or not produced into a peri- 
thecium; thalloid exciple frequently present. 
Apothecia surrounded by a thalloid exciple. 
Thalloid exciple well developed. 
Spores commonly simple. 
Algal cells blue-green, in clusters (Gloeo- 
capsa?); thallus inconspicuous, black- 
ish, sometimes coralloid............. 
Algal cells bright green (Cystococcus); thal- 
lus seldom blackish. ................ 
Spores 2-celled. 
Spores hyaline, the cells usually polar; 
thallus commonly more or less yellow- 
Spores brown, the cells not polar; thallus 
of various colors............-......-.- 
Thalloid exciple doubtful or evanescent. 
Spores simple. 
Spores minute and numerous in each ascus; 
apothecia usually immersed and the 
thalloid exciple uncertain. ........-. 
Spores very large, 1 to 8 in each ascus; 
apothecia embedded in verrucae, and a 
thalloid exciple rarely discernible... . 
Spores not simple. 
Spores hyaline. 
Spores 2-celled; the thalloid exciple ev- 
anescent or uncertain.............-- 
Spores more than 2-celled. 
Spores fusiform-acicular, 4 to 6-celled; 
the thalloid exciple inconspicuous 
or absent.................2.---- 
and one species of 
Spores cylindrical, elongated, many- 
celled; thalloid exciple usually 
evanescent...........---------- 
Spores not usually hyaline, muriform, 
many-celled; apothecia usually im- 
mersed.......2---.2----2-----2------- 
and one species of 
Apothecia without a thalloid exciple. 
Apothecia rounded. 
Spores hyaline. 
Spores simple. 
Spores either very large or very minute. 
Spores very large and one in each as- 
cus; thallus roughened or verru- 
CO 
Spores very minute and many in each 
ascus; thallus commonly granular 
and inconspicuous............... 
Spores medium-sized, 8 in each ascus; 
thallus granular, verrucose or areo- 
PyRENOpPSIS (p. 143), 
Lecanora (p. 171). 
PLacopiuM (p. 211). 
RINODINA (p. 220), 
ACAROSPORA (p. 170). 
PERTUSARIA (p. 187). 
GYALECTA (p. G1). 
HAEMATOMMA (p. 185). 
SECOLIGA (p. 62). 
CONOTREMA (p. 63). 
URCEOLARIA (p. 231). 
SECOLIGA (p. 62). 
MEGALOSPORA (p. 81). 
BIATORELLA (p. 65). 
LECIDEA (p. 67). 
43 
