M. FOSLIE. [1902 



Channel Rocks near Seattle, Wash , here anastomosed with L. 

 Soncleri 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 grovv 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 fi in diameter, or more frequently verti- 

 cally elongated, 12 — 24/^ long and 9 — 18 fi 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 f* 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 



