456 BULLETIN OF THE BUREAU OF FISHERIES. 
cases. The characters which are most useful for separating the species and have been 
used by recent authors are the mutual arrangement of the sori and the lines of hairs, 
the presence or absence of an indusium covering the sori, and the number of cell layers 
in the thallus. 
Fig. 20.—Elachistea stellulata, internal filaments branched Fig. 22.—Padina vickersia, cross section of thallus, X 273. 
and anastomosed, X 273. Fig. 23.—Goniotrichum alsidii, X 300. 
Fig. 21.—Elachistea stellulata, external filaments and “plu- Fig. 24.—Erythrotrichia carnea, cells forming spores, X 400. 
tilocular sporangia,” arising from basal disk as seen in optical 
section, X 273. 
Padina vickersie Hoyt. Fig. 22; Pl. XCII, figs. 1 and 2; Pl. CXIV, figs. 1-3. 
Zonaria variegata, Kuetzing, 1859, Bd. 9, p. 30, pl. 73, fig. 2. 
Padina veriegata, Vickers, 1905, No. 66. 
Padina variegata, Vickers, 1908, pl. 8. 
Padina vickersie, Hoyt, in Britton and Millspaugh, 1920, p. 595. 
Thallus erect, flat, expanded, 4 to 22 cm. tall, 5 to 37 cm. broad, entire when young, when mature 
repeatedly more or less deeply laciniate from the margins into segments, varying from cuneate spatulate 
to fan shaped, sometimes incrusted with lime, zonate by piliferous lines parallel with the margins, 
often becoming inconspicuous in the older parts, interpilar zones 1.5 to 6 mm. wide, base consisting 
of a thickened, rounded stipe 3 to 12 mm. long, densely covered with brown rhizoids, attached by a 
basal disk; lamina consisting of 3-cell layers near revolute apical margins, of 4-cell layers throughout 
most of thallus, and of 6 to 8 cell layers toward the base, epidermal cells about half as long as the central 
cells; tetrasporangia covered by a thin, subpersistent indusium, borne on both surfaces, usually pre- 
dominantly on the lower surface, occurring in 1 to 2 lines parallel with the apical margin about the 
middle of each interpilar zone, these lines frequently being broken, the tetrasporangia being scattered 
