, acicular spores (Fig. 6).
_Buellia_ and _Rhizocarpon_ are aberrant genera, brown-spored, and
closely related among themselves (Figs. 8, 9, and 13). Through
_Buellia_, the two genera are related to _Rinodina_ of the
_Physciaceae_. The two aberrant genera are like other members of the
_Lecideaceae_ with respect to thallus development and general apothecial
characters, the aberrancy being with respect to the spores, on which
account the two genera are placed in another family, the _Buelliaceae_,
by some workers, perhaps with sufficient reason.

The algal host is _Pleurococcus_-like (Fig. 2, c) in nearly all species
of the _Lecideaceae_; but the host cells are so hypertrophied and
distorted that their generic rank is often difficult to ascertain,
except by cultivation outside of the lichen thallus. The algal-host
cells are few in number in some of the species and are sometimes absent
during a portion of the life history of the lichen. The host is usually
found throughout the superficial portions of the thallus, except near
the upper surface, from which portion the algae are usually absent,
except in a dead or dying condition, difficult to detect.

The writer has collected the _Lecideaceae_, with other fungi, in Butler
County for fifteen years, and has worked for the Ohio Biological Survey
in Preble, Warren, Highland, Fairfield, Adams, Hocking, and Lake
counties. Besides these collections made by the writer, a few specimens
were examined from Champaign, Hamilton, Wayne, Morgan, Madison,
Muskingum, Franklin, Vinton, and Summit counties. Of the 37 species
treated in this paper, 24 had not been reported from Ohio previously.

[Footnote A: Contributions from the Botanical Laboratory of Miami
University.--XVIII]

_Systematic Account._

LECIDEACEAE

Thallus crustose, without plectenchymatous cortex (Fig. 2, a), varying
from granulose and often evanescent to conspicuous, areolate, or even
subsquamulose conditions, attached to the substratum by hyphal rhizoids
(Fig. 2, d), and in a few instances extending up as a veil and
surrounding the apothecia laterally, the hyphae densely interwoven
toward the upper surface, but more loosely disposed below (Fig. 2, a and
b); apothecia usually minute or small, commonly rounded, the exciple
weak and obscure (Fig. 10, d), or more strongly developed when
conspicuous and much darker in color (Fig. 11, b); hypothecium varying
from hyaline to dark brown (Fig. 10, b and Fig. 11, c); hy