OF CEYLON AND INDIA. 
375 
thallus, small it is true, but leading on to the type we shall 
now have to consider in Hydrobrynm. The dorsiventrality 
of this genus is not very marked, other than in the thallus ; 
the flowers, however, are very dorsiventral in structure, 
though the secondary axes stand erect ; as yet, however, 
we only know the plant at its flowering season. It seems a 
plant ill-adapted to water that is, or is liable to be, shallow. 
HYDROBRYUM. 
[(Endl.) Tul. ; Willis, Rev. Pod. Ind., Ann. Perad., I., p. 285.] 
As explained in the preceding paper, I have defined this 
genus, which has undergone many changes, practically in 
the same sense as that of Tulasne. Its most interesting 
species is perhaps H. olivaceum, which has caused much 
confusion by its peculiar habit and mode of growth. It has 
bf^en described by Warming (42, lY.) under its own name 
from Ceylon material, and in the same paper under the name 
Dicræa apicata from Nilgiri material ; neither description is 
exhaustive, and there is much to add. I have been able to 
study most of the species in the living condition, with the 
exception of H. Johnsonii, of whose autonomy I feel doubtful, 
and H. sessile, a new species discovered by Mr. Barber, but 
of which he kindly sent me abundant spnrit material. The 
genus is apparently confined to Asia, where it is common 
in suitable places. 
Hydrobryum lichenoides, Kurz. 
(Plates XXVIII., XXXI., XXXII.) 
This species occurs in numerous forms, nearly all of which 
I have studied on living material, in Ceylon and India. The 
plant shows a most remarkable amount of variation in 
many of its characters, and these variations seem to be 
different at almost every locality, so that it probably may be 
divided into a great number of varieties, even if it be not 
necessary to split it ultimately into several species. For the 
