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 mclagoniitui. 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<z mm. diam., 100 /A (8 cells) thick; sporangia 10-14 //. diam., 

 17-28 \t. long. In old fronds of Turnerella Pennyi. Fig. 97. 

 Greenland. 



Distinguished from Ulvella by the presence of setae ; from 

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

 by the filaments penetrating the host plant. 



19. GONGROSIRA Kiitzing, 1843, p. 281. 



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, occupjdng nearly all the cell wall, with one pyre- 

 noid ; asexual reproduction b} r 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, PL 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 ^ diam., 1-2 diam. long; membrane at 

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



