mplex spores.
With the advance in these two directions has gone a slightly increased
development of the thallus.

In structure, the thallus is crustose, and the thalli vary from
inconspicuous, evanescent conditions to those which are conspicuous and
sometimes even subsquamulous. Rarely the thallus extends upward as a
veil which surrounds the apothecia laterally and suggests how the
thalloid exciple of higher families probably arose. As usual in crustose
forms, the thalli are composed of hyphae which are densely disposed
toward the upper, exposed surface and more loosely disposed toward the
lower surface (Fig. 2).

The apothecial evolution passes from forms with weak, light-colored
exciples and soft texture (Fig. 10) to those with strong, dark exciples,
which are firm in texture (Fig. 11). The superficial apothecial
characters are so much alike in many of the species that one cannot
always feel certain even of the genus of unfamiliar forms until he has
studied them microscopically.

The paraphyses are commonly distinct in young apothecia, but in mature
apothecia they are usually more or less gelatinized and coherent. In
some of the species, they become so gelatinized that they form a
homogeneous mass about the asci, in which the individual paraphyses are
no longer discernible. When distinct, the paraphyses are sometimes
branched, most commonly toward their apices (Fig. 1 and 12).

There is great diversity with respect to spore development, the whole
range of spore structure, from minute, simple, hyaline spores to those
which are large, brown, and muriform being found within the family
(Figs. 3, 4, 5, 6, 7, 8, 9, and 13). This condition makes it appear
quite possible that the family may be polygenetic.

The genus, _Biatorella_, contains non-lichen forms and is probably as a
whole more closely related to the _Patellariaceae_ than to the
_Lecidiaceae_. However, our two species, both of which are lichens, are
herein admitted to the latter family. Through one or more species with
larger spores than are usually found in this genus, _Biatorella_
approaches _Lecidea_. Starting with _Lecidea_, we have a natural series
in spore development with intermediate conditions difficult to place.
The series runs thus: _Lecidea_ with simple hyaline spores (Fig. 3);
_Biatorina_ with two-celled, hyaline spores (Fig. 4); _Bilimbia_ with
several-celled, hyaline spores, not much narrowed (Fig. 5); and
_Bacidia_ with several-celled, hyaline