Evans: HEPATICAE OF Puerto Rico 535 
in the degree of complexity which it exhibits. Much of this ap- 
parent variation, however, is simply due to imperfect development. 
Ina normal lobule an inflated basal portion and plane outer portion 
may be clearly distinguished. The basal portion dilates abruptly 
from a short line of insertion and is strongly involute, the free 
Margin thus coming into contact with the lobe. In this way a 
distinct water-sac is formed, which sometimes includes the greater 
part of the lobule. The sac often bulges forward considerably 
beyond the short basal line. The plane outer portion of the lob- 
ule beyond the sac is bounded by the sinus, which separates 
slightly from the lobe, thus opening up into the sac a passage-way 
along the keel. The sinus is usually straight or nearly so, but 
sometimes shows a rounded or blunt angle. If the involute por- 
tion of the free margin is spread out, a slight indentation will be 
found between its outer extremity and the beginning of the sinus. 
This indentation is bounded by two projecting cells between which 
athird cell is situated, sometimes at the bottom of the indentation, 
sometimes extending forward as far as the projecting cells them- 
Selves but in a different plane. The hyaline papilla is borne upon 
this third cell and is usually curved inward and concealed within 
the water-sac (FIGUREs 6, 7). Apparently the cell which bears the 
papilla is homologous with the apex of the lobule as seen in other 
Lejeuneae. At any rate the lobule of a perigonial bract, which 
is normally acute and tipped with a single cell, bears a papilla 
upon this cell. The keel of the lobule varies greatly, being some- 
times straight or slightly arched throughout, sometimes distinctly 
mcurved near the base and arched in the outer portion. 
The leaf-cells have firm and pigmented walls and often bulge 
slightly on the outer surface of the lobe. Their trigones (FIGURE 
5) are usually distinct but vary greatly in size even ona single 
Plant ; they are of the triradiate type, and the ends of the rays are 
Separated from one another and from the frequent intermediate 
thickenings by narrow pits. Ocelli are not developed. The cell- 
Structure on the whole resembles that of Lopholejeunea and of 
S€veral other genera of the Lejenneae. 
The underleaves in Symbiesidium are relatively large and are 
Sometimes scarcely surpassed in size by the leaves themselves. 
They are attached by a strongly arched line of insertion and are 
