i6o Alexander W. Evans, 



Stephani cites the species also from Peel Inlet, Skottsherg (32, p. 

 6, as Aneura aiitoica). 



In R. autoica a type of thallus is met with that stands in sharp 

 contrast to those already described. The distinctive features will 

 be brought out in the following account, but it may be noted at once 

 that the plants have a distinctly prostrate axis, closely adherent to 

 the substratum by means of rhizoids. They are therefore either 

 scattered or grow in depressed mats. The type material is appar- 

 ently free from admixture. The plants are delicate in texture and 

 pale yellowish green in color, sometimes becoming brown with age. 



The axis is flattened and turns either the ventral surface (Fig. 7, 

 A, B) or an edge (Fig. 7, C) to the substratum. It exhibits long- 

 continued growth but in some cases at least the growth is eventually 

 limited, the apical portion curving away from the substratum and 

 developing directly into a photosynthetic branch-system. A typical 

 axis is 1-1.5 cm. long, 0.4-1 mm. wide, and 0.25-0.3 mm. thick. 

 The upper surface is plane or nearly so but the lower surface is 

 distinctly convex. Toward each side there is a gradual thinning 

 out, the edges being either rounded or bordered by a wing two or 

 three cells wide. These features are brought out with especial 

 clearness by cross sections, which show a plano-convex outline 

 with rounded (Fig. 7, E) or acuminate (Fig. 7, D) ends. It 

 often happens that one edge is winged and the other rounded. 

 This condition is sometimes associated with an axis turning one 

 edge to the substratum, but it may be associated with an axis 

 turning its ventral surface to the substratum. A well-developed 

 axis is nine or ten cells thick in the median portion. The surface- 

 cells average about 50 x 30 /x and the interior cells are usually 80- 

 i50jLilong but only 30 /x, wide. The cross section therefore shows 

 little or no contrast in size. The surface-cells are thin-walled 

 throughout ; the interior cells have very slightly thickened walls. 



The primary branches usually arise at intervals of 0.6-1.5 mm. 

 on each side of the main axis (Fig. 7, A-C). Not infrequently a 

 primary branch is prostrate and essentially like the main axis. In 

 many cases, however, a primary branch gives rise at once to a 

 photosynthetic branch-system, which spreads away from the sub- 

 stratum. Such a system, whether primary or secondary in origin, 

 is quickly limited in growth; it attains a length of 2-3 mm. and 

 is nearly or quite as wide as the axis. In the most typical cases 



