Evans: HEpATICAE OF Puerto RIco 21] 
PRIONOLEJEUNEA 
The genus Prionoleyeunca comprises a group of closely related 
species, all of which are found in moist tropical forests. It attains 
its highest development in America, but a few species from western 
Africa have recently been described. No species are known with 
certainty from Asia or from the islands of the Pacific. In their 
choice of a substratum the species are much less particular than in 
either Odontolejeunea or Cyclolejeunea. Some of them occur on 
rocks, others on rotten logs or on trees, still others on the roots 
and bases of tree ferns; in some cases the same form may be 
found on various substrata. Nearly all of them show a tendency 
to creep over tufts of larger mosses and hepatics, and it is most 
unusual to find a patch composed of a single species free from 
admixture of any sort. 
The species are all small and delicate and are pale green or 
yellowish in color. The characters derived from the leaves are 
extremely uniform throughout the genus. The lobe spreads 
widely from the axis and is attached, very much as in Harpale- 
Jeunea, by an almost longitudinal line of insertion decurrent by a 
single cell. Just beyond the lobule the lobe is abruptly dilated 
into a broadly ovate or orbicular expansion (PLATE II, FIGURES 2, 
19), the margins both, antical and postical being more or less 
rounded. At the apex it is usually abruptly acute or apiculate 
but is sometimes obtuse or even rounded, and there is often con- 
Siderable variation in these respects even in a single specimen. 
The middle part of the lobe is convex but the margin is plane and 
appressed to the substratum, thus leaving a small capillary space 
underneath the lobe. Except in a single species the margin of 
the lobe is distinctly crenulate or denticulate. Each tooth is 
commonly a single projecting cell (PLATE 10, FIGURE 22; PLATE 
II, FIGURE 21); in some cases every marginal cell forms a tooth 
of this character, in other cases the teeth are separated from one 
another by cells which do not project: sometimes a few of the 
teeth will be larger than the others and composed of two or three 
cells apiece. The denticulation of the leaves is subject to a great 
deal of variation even on a single individual, and the characters 
derived from the marginal teeth must therefore be used with the 
utmost caution in distinguishing between near allies. 
