Subgen. Pliostroma Fosl. mscr. 

 (sub Melobesia). 



Thallus inter conceptacula stratis cellularum 5—12 compositus. 



In species typically developed of the Corallinacé genus Melo- 

 besia the thallus is monostromatic with mostly small cortical cells 

 vvhich form no continuous layer, but only occur solitary and each 

 only covering the foremost part of the subjacent cell.^) In parts 

 of the thallus in which conceptacles are developed, a slight growth 

 of thickening takes place. Here the layers of cells is usually two 

 or three, seldom four (e. g. sometimes in M LejoUsii). In old 

 forms of Eumelohesia and Heteroderma, with or vvithout hetero- 

 cysts, respectivcly, the conceptacles are often densely crovvded and 

 developed over the greater part of the thallus, and when several 

 thalli become confluent and form. a crust somewhat extended, the 

 main part is composed of the said number of layers of cells. 

 Then in most cases only the marginal parts are monostromatic. 



On the other hånd, there are species which, even at a younger 

 stage of development, but peculiarly when fully developed, only 

 show a narrow m.onostromatic marginal zone, while in other parts 

 of the thallus there is a stronger growth of thickness. These parts 

 are composed of five to twelve layers of cells by a thickness of 

 up to 150 jj., even if the conceptacles are not crowded. When 

 several thalli are confluent or encompassing, for instance, a terete 



1) In one species, M. suhtilissit)ia, I have l'ound no cortical cells, and in 

 another, M. minutula, they seem partly to be wanting, partly to occur in 

 very small number. Of these species, hovvever, I have only had a scarcc 

 material. 



