255 



The outer pari of the sporangial conceptacles (fig. 174 E) is low, wart-like, with 

 plane upper face. The outer diameter of the conceptacle is often difficult to state, 

 as it is usually for a great part sunk in the frond, and the outer delimitation often 

 indefinite. One to three layers of cells are present under the conceptacle. The 

 roof is flat, thick, about 5 cells thick. The ostiole is clothed with numerous well- 

 developed unicellular hairs, the uppermost of which are long, and protruding out- 

 side the ostiole; the undermost ones are shorter and more oblique or horizontal. 

 They are all intensely stained by hsematoxyline. The sporangia do not occupy the 

 central portion of the 

 conceptacle, where a 

 small columella of 

 sterile cells is some- 

 times to be found. 

 The ripe sporangia 

 are always tetraspo- 

 ric. A small stalk- 

 cell is present under 

 the sporangia (not 

 shown in the figure). 



The antheridial 

 conceptacles (fig. 175 

 A) much resemble 

 those of M. subplana 

 (comp. fig. 161), being 

 provided with a simi- 

 lar tube, and the an- 

 theridia having the 

 same shape and posi- 

 tion as in that species. 



The cystocarpic conceptacles (fig. 175 B, C) have the same shape and size as 

 the sporangial ones, and the ostiole is endowed with a similar peristome. The thick 

 roof is plane, or a little depressed near the ostiole. The carpospores are, as usually, 

 produced seriately at the periphery of the conceptacle. 



The species appears fairly distinct from all hitherto described species of the 

 genus Melobesia. The low conceptacles with the thick, flat or a little deepened roof 

 distinguish it from other species of the genus having a well developed peristome 

 (e. gr. M. Lejolisii, coronata). Its occurrence on mollusc shells, unusual for the 

 genus Melobesia, might seem grounds for placing it in the genus Lithophyllum \ 

 the want of transversal pores between the frond cells and the fact that these 

 cells are not arranged in transversal rows, however, preclude its adoption in that 

 genus. 



Locality. Lf: S0nclre Ran by Lemvig, near the surface of the water, September. 



Fig. 175. 



Melobesia I richostoma. A, vertical section of antheridial conceptacle. B and C, vertical 

 sections of cystocarpic conceptacles. A and C 350:1. B (55:1. 



