Evans : Hepaticae of Puerto Rico 275 



incurved. The apex is usually broad and blunt but is frequently 

 abruptly apiculate or acute. In some cases the margin of the lobe 

 is entire throughout or indistinctly crenulate from projecting cells, 

 in other cases it is more or less toothed, especially in the apical 

 region, and in a few species it is sharply spinose. The leaves are 

 exceedingly variable in certain species, and the degree of mar- 

 ginal dentation must always be used with caution as a diagnostic 

 character. 



Except near the base of the lobe, the leaf-cells are mor^ or less 

 convex, and their walls are strongly thickened throughout The 

 middle lamella appears as a fine but distinct line and is clearly 

 visible without the use of reagents (plate 19, figures 5, 15}. 

 The thickening is deposited upon this lamella in the form of a 

 layer and is practically uniform over both horizontal and vertical 

 walls except for the scattered pits connecting the cells (figures 6, 

 16), Viewed from the surface of the lobe, the thickenings appear 

 in the form of large and often confluent trigones with occasional in- 

 termediate thickenings. The degree of thickening often varies in a 

 single species, and is apparently dependent upon external conditions. 

 Ocelli can frequently be demonstrated ; they differ from ordinary 

 cells in their larger size, in their thin walls and in their more oily 

 contents (plate 20, figure 7). In the majority of the species they 

 occur singly or in small irregular groups near the base of the lobe, 

 but in at least one species they form a short row simulating a 

 nerve. In certain species, the number and even the occurrence of 

 ocelli is subject to variation, some of the leaves failing to develop 

 them altogether. 



The lobule when normally developed conforms very closely 

 to that described for Prionolejetinea and for certain other genera 

 of the Lejeuneae, the hyaline papilla being proximal in position 

 ^ and the apical tooth short and curved (plate 19, figure 18 ; plate 

 20, FIGURES 10, 1 1, 24). The free margin of the lobule is involute 

 to beyond the apex and appressed to the lobe, the apical tooth 

 and the sinus helping to form the opening into the water-sac. 

 The lobule is inflated throughout and is more or less curved in 

 the outer part (plate 19, figures 12, 13; plate 20, figures i, 



3, 19)- 



The type of lobule just described is, however, subject to 



