6 M. FOSLIE. aa [1902 - 



Channel Rocks near Seattle, Wash, here anastomosed with L. 
Sondert f. pacifica (Setchell and Gardner, No. 654 in part). 
Lithothamnion conchatum Setch. et Fosl. mscr. 
Thallus forming plane or arching discs 0.5—1.5 cm. in diameter 
on Cheilosporum; conceptacles of sporangia subprominent, 0.7—1 
mm., conceptacles of cystocarps subhemispheric-conical, 0.6—0.9 
mm. in diameter. | 
If the hostplant, Cheilosporum, do not grow in too dense and 
irregular tufts and the species thereby being allowed to develop itself 
freely, it forms more or less plane and orbicular, about 0:5 mm. 
thick discs, partly shallowly undulating, partly not, and now and 
then feebly crenate. The plant is attached to the host in the lower 
central part, and in the free lower part most often being concentric 
zonate. The margin is sometimes and most frequently bent a little 
downwards, sometimes however upwards. This is what may be 
considered the typical form of the species. Often, however, more 
crusts are founded close to each other, become at length confluent 
and form clustered, more or less imbricate crustcomplexes over 
some branches of the host, partly attached with the whole lower 
part, partly here and there free, or, not seldom, more or less arching 
crusts form almost similar’crustcomplexes nearly surrounding certain 
parts of the hostplant. Now and then a crust becomes propor- 
tionally thick and lumpy, up to 1.5 mm. in thickness, or almost 
square or angular, occasionally even with a short stalk. | 
A median section of a typically developed crust shows, that 
it is attached to the host with a rather feebly developed, coaxillate 
hypothallic layer, the latter sending forth perithallic rows of cells 
which are square, 9—15 p in diameter, or more frequently verti- 
cally elongated, 12—24 » long and 9—18 p broad. In the freely 
developed part of the crust the hypothallic layer is frequently more 
vigorously developed, composed of cells which are most often 
20—40 p» long, and sends forth upwards perithallic rows corre- 
sponding with the mentioned ones, but in somewhat thick crusts 
even downwards too. 
The conceptacles of sporangia are crowded over the whole 
