No. 1 1] PLIOSTROMA A NEW SUBGENUS OF MELOBESIA. 5 



section the cells are subquadrate, slightly horizontally or vertically 

 elongated, 7 (6)— 18 by 7 — 16 /^t. The conceptacles of sporangia 

 are scattered or somewhat crowded, convex or convex-conical, 

 140—250 (300) iJ. in diameter, when seen from above. The con- 

 ceptacles of cystocarps are of about the same size. The sporangia 

 are tetrasporic, 45 - 60 jj. long and 30—40 /i broad. 



The species proves to be very nearly connected vvith M. Lejo- 

 lisii, from which it is distinguished essentially only by its greater 

 thickness and by a little narrower cells which are more frequently 

 somewhat elongated in the direction of the radius. It occurs on 

 glass, china, and small shells. At Banyuls sur Mer some years 

 ago a Melobesia-\]kQ form was found on glass in the aquarium of 

 the laboratory Arago. Professor Sauvageau kindly sent me a 

 piece of such aquarium glass with numerous and particularly 

 young crusts of this calcareous alga on it. I tirst supposed that 

 it belonged to M. Lejolisii, but have later on come to the con- 

 clusion that it has to be referred to 31. sonalis. 



An authentic specimen of M. myriocarpa which I have seen, 

 corresponds in all essentials with typical M. zonalis. According 

 to Crouan, however, it is somewhat varying. I, therefore, as I 

 observed 1. c, take it in the sense that it corresponds to M. fari- 

 nosa f. Solmsiana and M. minutida f. lacunosa with a very irre- 

 gular, often subdichotomous thailus. The typical form I consider 

 as a more regular, sometimes almost circular one. 



M. zonalis occurs at Brest (Crouan!), Plymouth (Batters!) 

 and Banyuls sur Mer (Sauvageau!). 



Melohesia (Pliostroma) mauritiana Fosl. mscr. 



Lithophyllum (Carpolithon) mauritianum Fosl. Aig. Not. III (1907) p. 32. 



In this species the peripherical part of the thailus is mostly 

 irregular, crenulate or provided with short and rather narrow, 

 irregular offshoots. This part is monostromatic. The cells are 

 here, as seen from the surface, elongated in the direction of the 

 radius, 11-18 (22) // long and 6-9 (11) // broad. The cor- 

 tical cells are nearly linear, or oblong. The central parts of 

 the thallus attain to a thickness of about 80, and sometimes 



