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ing small, lanceolate, fan -shaped groups. From 

 the cells of the hypothallus rise more or less obliquely 

 ascending filaments: the perithallus. . . Subgenus Cmoriella. 



a. Thallus hard, calcareous, firmly adhering to the 

 substratum. 



1. Thallus very thin, when decalcified easily de- 

 tached from substratum and so small that it can 

 be expanded in toto on a slide ; colour dark pink. 



P. armorica Grn. 



2. Thallus much firmer, surface slightly marked 

 with small low elevations, sometimes with radial 

 lines but no veins ; perithallus with an inferior 

 part of large cells and a distinct superior part 



with small cells ; colour dark pink . . . P. Dubiji Grn. 



3. Thallus very firm, surface smooth but with di- 

 stinct veins running from the centre towards 

 the periphery ; perithallus with cells often almost 

 isodiametric except the basal large and the su- 

 perior small ones. Colour dark purple with a 

 green hue P. Boergesenii nov. spec. 



b. Thallus fleshy, slightly calcareous at base, firmly 

 adhering to substratum and tearing in horizontal 

 direction after having acquired a given thickness. 

 Inferior cells of the upper, torn off, part transform 

 into a new hypothallus ; colour probably pink . . . 



P. Nordstedtii nov. sp. 



II. Thallus procumbent, adhering more or less firmly to 

 the substratum, orbicular or irregular in outline, with 

 a hypothallus consisting of in the main straight, 

 juxtapposed, dichotomous filaments, running 

 from the centre towards the periphery, giving rise to 

 more or less obliquely ascending filaments : the peri- 

 thallus Subgenus Eupeyssonnelia. 



a. Thallus hard, calcareous, with short, high apical 

 cell. 



1. Thallus thin, consisting of 6, 7 layers of cells, 

 easily detached from substratum, mostly orbi- 

 cular with radial lines ; colour light pink .... 



P. simulans nov. sp. 



2. Thallus more robust, firmly adhering to the 

 substratum, colour purple 



P. conchicola Pice, et Grun. 



