FINK—THE LICHENS OF MINNESOTA. 101 
above; paraphyses distinct or cohering, sometimes branched and frequently thick- 
ened and brownish toward the apex; asci clavate or inflated-clavate; spores 2 to 
4-celled and becoming muriform, hyaline to blackish brown, 18 to 38 » long and 10 
to 17 » wide. 
Occurring rarely in the extreme northern portion of the State. On rocks. 
Throughout British America and Alaska and occasionally noted in the northern 
United States and southward in the mountains. Known in all the grand divisions. 
Buellia geographica of the preliminary reports. 
EXPLANATION OF PLATE 8.—See page 100. 
Family PSORACEAE. 
This is a small family closely related to the last. Indeed, it may well be doubted 
whether there is sufficient reason for separating the Psoraceae from the Lecideaceae. 
In the present family the thallus is squamulose or squamulose-crustose with a well- 
developed cellular cortex above, while in the Lecideaceae there is rarely any sug- 
gestion of a squamulose condition, and in these best states there is only rarely a 
suggestion of a cellular cortex, never one sufficiently developed to form a continuous 
layer. 
The apothecia are similar to those of the last family, but there is never any thal- 
loid exciple. The algal symbiont is Cystococcus, The spores do not show so wide 
a range of structure as in the Lecideaceae, the brown and muriform forms being 
wanting. 
Externally the thalli resemble those of certain Dermatocarpons, but there is no close 
relationship between that genus and members of the present family. 
Two genera and several species and subspecies of the family occur in the State, 
on rocks or earth. The first genus seems to stand between section Biatora and 
Cladonia, while the second is nearest to Eulecidea, except for the spores, which are 
nearer to those of Bilimbia. 
PSORA Hoffm. Descr. Pl. Crypt. 1: 37. pl. 8. f. 1 (et seq.) 1790. 
PLATE 9. 
The thallus is composed of squamules, each of which is to be regarded as a small 
foliose structure. These squamules are of various forms and may be scattered 
or may be run together into a continuous crustose or foliose thallus. The upper 
cortex is well developed and thick and shows a more or less well-defined cellular 
structure in all of the species. The lower cortex may be entirely wanting, or there 
may be a pseudocortex of hyphze extending for most part in a horizontal direction. 
The algal layer is always well represented. When the pseudocortex is present on 
the lower side, it replaces the medullary layer. The upper cellular cortex is more 
or less gelatinized and the cell lumina correspondingly reduced, and the gelatiniza- 
tion may go so far as completely to obliterate the cellular structure, especially in the 
upper portion of the cortex, The algal symbionts are doubtless a form of Cystococ- 
cus. The color of the thallus varies greatly. The squamules are attached to the 
substratum by more or less numerous hyphal rhizoids; and they may be flat and closely 
attached throughout, or the margins may be ascendant. 
The apothecia are variously disposed over the surface of the squamules and are rather 
small and adnate or sessile. The proper exciple is evanescent or soon overgrown in 
all of our species and is therefore seldom seen. The color is most commonly a brown or 
black. The hypothecium is usually more or less brown, and the hymenium pale or 
somewhat colored. The paraphyses are commonly simple, but branched forms may 
be found in any of our species. The spores are simple, ellipsoid in form, and hyaline. 
In apothecial and spore characters the present genus is plainly most closely related 
to Lecidea, but the thallus is much better developed than in any member of that 
