1919] Setchell-Gardncr : Myxophijceae 41 



penetrate into the substratum and whicli are more simple in their 

 structure. These in turn give off true branches. The structure tlius 

 far is stigonemataceous. There are no hormogonia, however, but seem- 

 ingl}^ coccogonia (cf. Bornet and Flahault, loc. cit., p. 22). There are 

 also distinct gonidangia whose contents divide into gonidia, sucli as 

 are found in the Chamacsiphonaceae. 



While the general appearance of Hyella caespitosa B. and F. differs 

 very much from that of RaclouM Gomantmna Sauv., yet it is by no 

 means a simple matter to place certain Californian plants recently 

 described. Gardner (1918, p. 432) has stated these difficulties and 

 has outlined his reasons for placing some under Hyella, as follows : 

 "These forms with erect filaments, more or less branched and dis- 

 torted, arising from basal filaments on the surface of the substratum, 

 and growing into it, and having gonidangia at their bases near the 

 surface of the host, have been assigned to Hyella." 



The genus Hyella is credited by Forti (1907, pp. 124-127) with 

 five species, the type (//. caespitosa.) and three others being shell 

 borers, while the fifth burrows ( ?) into certain red algae. Of the four 

 species thus far detected on the Pacific Coast of North America, two 

 are shell borers and two burrow into membranous red algae. 



Key to the Species. 



1. Boring into shells 2 



1. Partially endophytic on larger algae 3 



2. Erect filaments usually less than lOft in diam 1. H. caespitosa (p 41) 



2. Erect filaments 10-14/u. in diam 2. H. Littorinae (p 42) 



3. Filaments branching dendroidally 4. H. socialis (p 44) 



3. Filaments seldom branching 3. H. linearis (p 43) 



1 . Hyella caespitosa B. and F. 



Colonies appearing at first as minute discolorations on shells, later 

 becoming much expanded and confluent, frequently covering the 

 entire outer part of the shell, causing it to be very rough ; erect fila- 

 ments usually parallel, 5-6/t, even up to lO^u, diam., lOO-200/i long, 

 lower cells shorter, and ujipcr (mes several times longer than the 

 diameter and sometimes branching; sheaths hyaline; horizontal 

 filaments much branched, composed of spherical or angular cells, often 

 several rows in a sheath ; cell contents yellowish olive green or blue- 

 green; gonidangia formed by the modification of cells towards the 

 base of the filaments into large oval to pyriform gonidangia, gonidia 

 numerous, spherical, about 2/a in diameter. 



