Puate CCCLVII. B. 
DUMONTIA FILIFORMIS, Grev. 
(See description under Pirate LIX.) 
The analysis in Pl. LIX. fig. 2 and 3, and the generic cha- 
racter, are both faulty. It is hoped that the figures now given 
will show the proper structure of the walls of the frond, and the 
position of the fructification ; and the following emended generic 
character is offered :— 
Gen. Car. Frond tubular; the tube at first occupied by a lax network 
of longitudinal, anastomosing filaments; at length distended and 
empty. Walls composed of longitudinal, anastomosing filaments, 
emitting toward the circumference dichotomous, moniliform branches, 
which form a middle stratum ; cortical stratum composed of a single 
layer of small cells. Favelle roundish, formed by a metamorphosis 
of the dichotomous branches. Tetraspores dispersed, cruciate, with 
wide limbs, sunk beneath the cortical stratum, formed of one of the 
cells of the dichotomous branchlet. 
From this it will be seen that Dumontia has nearly the same 
structure as Catenella, omitting the constricted branches. The 
statement made under Pl. LIX. that I had seen no tetraspores 
of this common plant, has brought me specimens from several 
kind correspondents, to whom my thanks are due. At the same 
time (to my shame be it spoken) I find, on examining some old 
specimens collected in 1832, that I ought to have made no such 
statement, and further, that the ¢efraspores of this Alga are 
very common. It sometimes happens that botanists are less 
acquainted with the structure of very common than of rarer 
plants, and in this instance I have to plead guilty to a careless 
want of observation. 
B. Fig. 1. Vertical slice of the wall of DuMont1Ia FILIFORMIs, with ¢etraspores. 
2. Small portion of the same. 3. Vertical slice of a specimen with favelle. 
4. Small portion of the same :—all the figures more or less highly magnified. 
