163 
to very short-rostrate ; columella persistent; peristome double ; 
the teeth united at the base, linear-lanceolate, slender pointed, 
closely and regularly articulate, with a very distinct median line, 
darker colored and marked with very fine transverse lines below, 
above lighter and granulose-roughened. Segments lanceolate, 
attached to a wide basal membrane, more or less split along the 
keel, granulose-roughened above, usually brownish yellow; cilia 
two or three, well developed, nodose or appendiculate (except in 
the four species mentioned above). Spores some shade of brown, 
nearly smooth to very finely roughened. 
The roughening of the spores and the transverse lines on the 
peristomal teeth are so fine that a magnification of 300—400 di- 
ameters is required to bring out these points wel 
The genus can be divided into six fairly distinct groups. 
I. Salebrosum group including B. sa/ebrosum, B. ffexicaule, B. 
campestre, B. Roteanum, B. acutum, B. oxycladon, B. albicans, B. 
pseudo-collinum and B. turgidum. 
Il. Rutabulum group including B. rutabulum, B. asperrimum, 
B. lamprochryseum and B. rivulare. 
III. Acuminatum group including B. acuminatum, B. splen- 
dens, B. biventrosum and B. cyrtophyllum. 
IV. Plumosum group including B. plumosum, B. populeum 
and P. digastrum. 
V. Reflexum group including P. N B. glaciale, B. 
Starket and B. Novae- Angttae. 
VI. Velutinum group including B. velutinum, D. Leibergu, B. 
Idahense, B. sub-erythrorrhizon, B. collinum, B. Utahense, B. ery- 
throrrhizon and B. Bolanderi. 
I. Costa extending into apex. 
Seta ed rough throughou 
s very slender ; a cells 3-5:1 21. B. reffexum. 
piah more robust; leaf-cells I n 22. B. glactale. 
Seta nearly smooth at we leaf-cells é . B. po 
. Costa nig S -24 ie a leaf. 
1. Branch leaves entire. * 
Branch leaves long-filiform acuminate. 
Slender. 
, dioicous. 7. B. albicans. 
Very stout, monoicous. ? 9. B. turgidum. 
Branch leaves narrowly acute to acuminate. I8. B. plumosum. 
*The branch leaves of B. acutum are often entire. 
