202 



As above mentioned the thallus consists of two layers of 

 cells, a thinner one with nearly rectangular cells upon the sur- 

 face (Fig. 153 c, e), and a layer of larger cells below. The whole 

 thallus has a thickness of about 90 /j, the cells of the surface of 

 about 35 ju. In the basal part the cells have thick walls (Fig. 

 153 b) and are of nearly the same size upon both side of the thallus ; 

 from both cell-layers numerous rhizoids grow out forming a dense 

 cover and below the attachment-disc. 



Series of hairs occur upon both sides of the thallus but most 

 richly upon the upper surface. 



In several respects this species very much reminds one of 

 P. gymnospora having nearly the same arrangement of the tetra- 

 sporangia though with the difference that the upper series of 

 hairs occur at some distance from the tetrasporangia ; further it 

 differs in the presence of the indusium and by the distromatic 

 thallus. 



This species has only been found once in the upper sublittoral 

 region in a somewhat exposed place. 



St. Croix: Coaldey Bay. 



2. Padina gymnospora (Kiitz.) Vickers. 



ViCKERs, A., Liste des Algues de la Barbade (Ann. des sc. nat., Bot., 

 9e serie, t. I, 1905, p. 58); Phycologia Barbadensis, pi. VII. Weber-van 

 BossE, A., Liste des Algues du Siboga, I, 1913, p. 178 — 180. 



Zonaria gymnospora Kiitz., Tab. Phycolog.; vol. IX, 1859, p. 29, 

 tab. 71, fig. II. 



To this species, originally described from St. Thomas I have 

 referred several specimens of which in the following lines I give 

 a more detailed description. 



In its upper part near the margin the thallus only consists 

 of two layers of cells namely upon the upward turned side a 

 layer of small cells, in transverse section nearly square, and 

 below a layer of larger cells, rectangular, higher than broad. The 

 thickness of the whole thallus is about 110;/, while the upper 

 small cells only reach about 35 fx in height and the larger cells 

 below about 75 fi. Lower down in the thallus the large cells are 

 gradually divided by a horizontal wall (Fig. 155 a) and the thallus 

 consists now of three layers of cells. It is the same also near 

 the base but here the cells of the lower face are also divided by 

 vertical walls into small cells similar to those of the upper sur- 

 face (Fig. 155 d). 



