genus, Dermatolithon, characterised by having a single apical pore in the hemisphe- 
rical-conical conceptacles, sporangia “with short foot rising from the almost plain 
disc” and developing, according to Rosanorr, between club-shaped (?) paraphyses. 
In 1904 (Algol. Not. I. p. 3) however, he comes to the conclusion that these charac- 
ters had not proved sufficiently constant, and did not form any distinct limit as 
against the genus Lithophyllum. He therefore no longer maintains Dermatolithon 
as a genus, but regards it as a sub-genus under the last-named genus, to which 
Heydrich had already previously (Corallinaceæ etc., Ber. deut. bot. Ges. 15, 1897, p. 47) 
reckoned Melobesia Corallinæ Crouan, and points out that it is further distinguished 
by its anatomical structure, the hypothallium being formed by a single layer of 
inclined cells. In 1909, (Algol. Not. VI, p. 57) however, it is again reinstated as a 
genus, FOSLIE now attaching greater importance to the mentioned anatomical char- 
acter, and it was adopted by SvepeLıus in 1911. M. B. Nicuozs, who has subjected 
some species of this relationship to closer investigation, (Univ. of California Publ. 
in Botany vol. 3, No. 6, 1909) discusses some of the other characters cited by FOSLIE, 
viz: the presence of a “plug” in the orifice of the sporangial conceptacles united at 
the basis by a parenchymatic tap; the position of the sporangia at the bottom of 
the conceptacle, which in Melobesia is said to be almost flat, in Lithophyllum over- 
arched; and the presence of a stalk cell under each sporangium in Melobesia. He 
adopts the standpoint which Foslie then adhered to; i. e. not maintaining Dermato- 
lithon as a genus, but referring the species concerned to Lithophyllum, (L. macro- 
carpum, pustulatum, tumidulum). He points out, however, that in so doing, “the 
characters which separate Lithophyllum and Melobesia are not sufficiently well marked 
to warrant two separate genera” (p. 361). With regard to the structure of the con- 
ceptacles and the organs of reproduction, there is doubtless great similarity between 
the two genera; at any rate, no thoroughgoing differences appear to have been de- 
monstrated up to now. The vegetative structure seems to me to present an ex- 
cellent distinctive character, as in Melobesia, we never find transverse pits between 
the upright cell-series proceeding from the basal layer, whereas such are present 
in all Lithophyllum species, including the subgenus Dermatolithon. On the other 
hand, transverse fusions are of common occurrence in the Melobesia species, but 
are wanting in Lithophyllum. This seems, as a matter of fact, to be the best 
distinctive character between the two mentioned genera. 
As to how far there may be reason to make further exclusions from the genus 
Melobesia, this must be left to further investigations to decide. Fostir, in 1900, 
(Rev. Surv. p. 21) established a subgenus Heteroderma, which he characterises as 
having the “thallus composed of more layers of cells” in contrast to Eumelobesia, 
which should have but one layer, except as regards the frond near the conceptacles. 
In 1905 however, (Remarks p. 102) a different limitation is made, and in 1909, (Alg. 
notes VI, p. 56) Heteroderma is raised to the rank of a genus, distinguished from 
Melobesia solely by the lack of hair-cells. I do not consider that we are justified 
in distinguishing between two genera merely by the presence or absence of hair- 
