74 



met wit h en stones (Fig. 30). The ernst clings closely and in general rather firmly to the 

 substratum, here and there however but loosely covering die Iatter and then developing few 



and short rhizoids. Smal] 

 crusts are fonned partly by 

 a solitary layer of cells. 

 partly, and most frequently, 

 by several ones, which is 

 the case particularly when 

 the plant forms extended 

 crusts. Such crusts attain 

 a thickness of up to about 

 2 mm., composed of numer- 

 ous smaller or larger layers 

 of cells, one upon the other, 

 partly anastomosed with the 

 subjacent, partly not and, 

 therefore, showing a more 

 or less scaly or irregular 

 surface. The plant often 

 alternates with other cal- 

 careous algae, or animals, 

 or it is rather mingled with 

 divers foreign bodies which 

 have been overgrown here 

 and there in the layers 

 (Fig. 31). Therefore, the shape of the crusts depends on that ot the substratum, and the 

 layers are in most cases very irregularly fonned on each other. 



In a vertical section ot the ernst the cells are shown to be somewhat varying in size, 

 partly large, partly rather small even in one and the same section. Thus fig. 31 A. exhibits 

 mostly large cells, about the largest ones which ocenr in this species, but in other parts of the 

 same section occur cells which are in part even a little smaller than those represented in 

 fig. 3 1 B. They are always vertically elongated, seldom nearly squarish, with thick walls and 

 usually a little rounded corners, varying between 30 and 60, or up to about 75 \x. in length 

 and 15(12) — 25, or up to 30 u.. in breadth. 



1 he conceptacles of sporangia, which are the only reproductive organs known, occur 

 scattered. They are superficial, conical and generally 0,8 — 1 mm. in diameter, when seen from 

 the surface. The sporangia are four-parted, 1 So — 250 u.. long and 100 — 150 u,. broad. The 

 conceptacles frequently at length become dissolved, leaving a more or less distinct scar which, 

 however, soon gets effaced. But sometimes new crusts partially extend themselves over the 

 conceptacles even before the Iatter are fully developed, or occasionally quite cover such ones 

 which are emptied and partly undissolved, partly being in a state of dissolution. Therefore, 



Fig. 30. Mastophora melobesioides Fosl. 



A. The type specimen from the Maldives; />', C, D. Specimens almost fully 



covering dead corals and other calcareous algae: Stat. resp. 303, 133, Si: nat. size. 



