I92.i| Set eh i ll-Giwdm r: Melanophyceae 491 



lateral outgrowths from the metamorphosed cells may occur. The 

 number of erect filaments in proportion to the number of gametangia 

 is a character which seems to be very unstable. In some collections 

 they exceed the number of gametangia almost two to one, in others 

 they do not occur more than in proportion of one to five. They are 

 very irregular in origin along the radiating creeping filaments. Some 

 near the margin of the frond may be nearing maturity before others 

 near the center of the frond have started. 



3. Hecatonema clavatum S. and G. 



Plate 53, figs. 1-4 



Fronds forming circular cushions 2-3 mm. diam., with relatively 

 wide margin free from erect filaments; prostrate portion attached 

 by numerous, short, subulate rhizoids, and composed of regularly 

 radiating, closely crowded filaments; erect filaments mostly clavate, 

 unbranched, 190-210//. long; cells of creeping filaments 5-6/x diam., 

 1.5-2 times as long; cells of erect filaments cylindrical below and 

 5. 5-6.5//. diam., 2-2.5 times as long, slightly constricted at the dissepi- 

 ments above and 8-11//. diam., 1.5 times as long; zoosporangia (?) 

 sessile or subsessile on creeping filaments, clavate, 60-80/a long, 10-1 4/i 

 broad ; gametangia cylindrical to slightly fusiform, sessile or on short 

 pedicels on the creeping filaments, 55-85//. (up to 111//.) long, 8-12//. 

 broad ; locnli mostly 2-seriate. 



Growing on the pneumatocysts of Nereoeystis Luetkeana. Mouth 

 of Tomales Bay, Marin County, California. 



Setchell and Gardner, Phyc. Cont. IV, 1922, p. 378, pi. 40, figs. 1-4. 



The structures designated zoosporangia (?) in the foregoing diag- 

 nosis of this species were found interspersed among the gametangia. 

 No indication of the formation of zoospores has been observed, which 

 leads to the suspicion that they may be abortive gametangia. The 

 terminal cell of the erect filaments is often longer than the cells 

 below it, and in these filaments in which the cells are divided length- 

 wise, producing the clavate condition, the terminal cell degenerates in 

 a similar manner as do the hairs in other species. The longitudinal 

 division of cells in the upper parts of the filaments is undoubtedly 

 connected w T ith the formation of the short, lateral, often secund, game- 

 tangia characteristic of nearly related species in Hecatonema and 

 in Compsonema, for in a few instances such gametangia were observed 

 in old specimens in wdiich the gametes had, to a large degree, escaped 

 from the characteristic gametangia. 



