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, 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.