NO. 1 TAYLOR: PACIFIC MARINE ALGAE 41 



Monostroma dactyliferum n. sp.^^ 



Plants small, 2-3 cm tall, dark green, irregularly lobed, the lower 

 portions stalklike; stalks 1-3 mm broad, irregularly branched, narrow, 

 thin near the markedly crisped margin but thick in the center (to 180- 

 200 fi) and tristratose, consisting of a layer of cells 50-60 ix tall and 20-30 

 fi broad on one side, a central zone one third of the total thickness or more 

 consisting of fibrillar extensions of the surface cells directed toward the 

 base, and on the other side a layer of cells about 20-30 fx, broad and 18-25 

 /i, tall; the upper portion of each branch for 1-2 cm eventually somewhat 

 expanded, simple to palmatifid, the lobes 3-5 mm broad, obtuse, the 

 margins plane to minutely lobulate and crisped, in the center about 15-20 

 fi thick, the cells in section rectangular, 11-16 fx tall and about as broad; 

 walls thick throughout, the cells in the expanded part somewhat areolate. 



These plants are extremely interesting. Structurally, the stalk some- 

 what resembles the base of an Ulva, except that the strengthening fibrils 

 pass abundantly between cell layers which are unequally thick; this fea- 

 ture extends up the stalklike portions to the thin blades. The margins of 

 these stalks are intricately frilled, much thinner than the central part and 

 of one cell layer. The specialized central zone develops along a sharp line 

 near the base of the blade. Here the thickness suddenly increases from 

 about 30 fjL to about 45 ju, and the cells, which are columnar, all cut off a 

 small cell toward the same face of the thallus. Gradually these cells, both 

 the large primary ones and the small derivatives, develop projections 

 which extend basipetally between the two layers. These, at first in con- 

 tact, become separated by a thick hyaline zone one third to one half of 

 the total thickness of the stalk, composed of tenuous protoplasmic fila- 

 ments surrounded by relatively firm walls. This structure is not a familiar 

 one in the genus, and a new one may have to be erected to contain this 

 species. The fibrils run down as a thin zone between equal cell layers in 

 Letterstedtia japonica Holmes, but in that plant the blades have two cell 

 layers throughout, as does JJlva. In studying the peculiar structure of M. 

 dactyliferum longitudinal sections were cut from carefully oriented frag- 

 ments under continuous observation with the dissecting microscope, which 

 enabled the zone of change to be established accurately. 



Ecuador: Guayas, in tide pools at Pta. Santa Elena, Schmitt no. 

 523 (TYPE), 17 Sept. 1926. 



■11 Monostroma dactyliferum n. sp. — Plantae 2-3 cm altitudine, irregulariter, 

 saepe digitate lobatae, stipites infra quo in loco ad 180-200 (.i crassitudine et, 

 cum strato medio rhizoideo, tristratosae; supra expansae, lobis 3-5 mm latitudine, 

 crispatis, in centre 15-20 |x crassitudine et unistratosis, cellulis distributione paulu- 

 lum areolatis. Planta typica in loco dicto Pta. Santa Elena, Guayas, Ecuador, legit 

 Schmitt no. 523, 17 Sept. 1926. 



