1920] Setcheil-Gardner : Chlorophyceae 223 



1. Spongomorpha arcta (Dilhv.) Kiietz. 



Plants rich green, in dense f astigiate tufts, up to 15 cm. high ; 

 filaments erect, stiff, 60-lOOju, diam. above, below smaller, much 

 branched ; branches erect or appressed, obtuse or clavate at tips ; seg- 

 ments above 4-6 diam. long, below 1.5-3 diam. long ; rhizoidal descend- 

 ing branches 40-60/x diam. with segments 2-6 diam. long, firmly mat- 

 ting together the lower part of the tuft. 



On rocks and on Fucus in the middle and lower littoral belts. 

 Alaska (Bering Sea) to Washington (Puget Sound). 



Kuetzing, Sp. Alg., 1849, p. 417 ; Collins, Green Alg. N. A., 1909, 

 p. 359 (excluding varieties). Conferva arcia Dillwyn, Brit. Conf., 

 1809, p. 67, pi. E. Cladophora arcta Kuetzing, Phyc. Gen., 1843, 

 p. 263 ; Harvey, Phyc. Brit., vol. 2, 1849, pi. 135 ; Setchell and Gard- 

 ner, Alg. N.W. Amer., 1903, p. 224 (in part and excluding varieties 

 except in part). Cladophora lanosa var. uncialis, Tilden, Amer. Alg. 

 (Exsicc), no. 372 (not of Thuret). 



We have referred a number of specimens to Spongomorpha arcta, 

 but without any knowledge of the exact nature of the type. The type 

 specimens came from Bantry Bay, on the southwest coast of Ireland, 

 and seem to be plants all of whose filaments are slender, obtuse or 

 clavate at the tips, decidedly matted together below by descending 

 rhizoidal branches but free and spreading in the upper portions. 

 Neither hook nor spine branchlets are present. The plants referred 

 here from our territory correspond in these general details and are, 

 at least, closely related to this species. We are left with the impres- 

 sion, however, that this may be the conception of a group of species 

 rather than of a single specific entity. 



We have been unable to divide the Spongomorpha arcta of our 

 coast into the varieties given by Collins in The Green Algae of North 

 America (1909, pp. 359, 360). His f. conglutinata, based chiefly on 

 the separation of groups of terminal filaments into " Symploca-like 

 tufts" and said to have "acute branches occasionally found at the 

 base of the older plants," proves to have, on careful examination of 

 the plants on which it is based, and which show the characteristic 

 habit, not only spiny branchlets but simple hooked branchlets as well. 

 We feel compelled, therefore, to refer these plants rather to Spongo- 

 morpha spinescens, at least as we understand that species in this 

 account. We find a similar combination of spiny branchlets and 

 hooked branchlets in no. 918 of Collins, Holden and Setchell 's Phj-co- 



