290 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



the tip ; the very narrow passage through the seta not parti- 

 tioned off from the cell ; zoospores have not been observed, but 

 the appearance of the fronds sometimes indicates that they are 

 probably formed in the superficial, bristle-bearing cells. On 

 Chaetomorpha mclagonium. Fig. 98. Greenland. 



This plant usually grows in company with Lithodcrma and 

 other epiphytic algae, which often so cover it that the develop- 

 ment of the setae is much obstructed. 



18. ARTHROCHAETE Rosenvinge, 1898, p. no. 



Frond epiphytic or endophytic, incrusting, orbicular, pseudo- 

 parenchymatous, sending towards the interior of the host plant 

 filaments which branch and spread in the medullary layer of the 

 latter ; superficial vegetative cells usually bearing each a long 

 seta, separated from the cell by a partition, and itself with one 

 or two partitions ; sporangia formed from superficial cells, con- 

 stituting a continuous layer, obovoid or cylindrical ; the zo- 

 ospores escaping by an opening at the top. Marine. 



Only one species. 



A. PENETRANS Rosenvinge, 1898, p. in, fig. 24. Frond to 

 \y? mm. diam., 100 /u, (8 cells) thick; sporangia 10-14 /* diam., 

 17-28 /A long. In old fronds of Turncrella Pennyi. Fig. 97. 

 Greenland. 



Distinguished from Ulvella by the presence of setae ; from 

 Chaetobohis by the articulate character of the setae, as well as 

 by the filaments penetrating the host plant. 



19. GONGROSIRA Kiitzing, 1843, P- 2 ^ 1 - 

 Fronds of densely packed, articulate, simple or sparingly 

 branched filaments, each attached by a disk-shaped expansion ; 

 cells about as long as broad or somewhat longer ; chromato- 

 phore parietal, occupying nearly all the cell wall, with one pyre- 

 noid ; asexual reproduction by biciliate zoospores, also by 

 akinetes. 



A genus long considered doubtful, and from which most of 

 the species have been removed ; but probably to be maintained 

 for the few remaining species. 



G. DEBARYANA Rabenhorst, Algen, No. 223; Wille, 1887, 

 p. 484, PI. XVIII, figs. 106-114; PL XIX, figs. 115-135; P. 

 B.-A., No. 1187. Filaments ascending, bright green, dichoto- 

 mous, forming an irregular expanded stratum ; cells of varying 

 shape, 15-30, rarely 40 /A diam., 1-2 diam. long; membrane at 

 first thin, becoming thick and lamellate ; terminal cell swollen, 



