30 University of California Publications in Botany [Vol.8 



no specimens of Sphacelaria from them, nor have we seen any speci- 

 mens of Saunders. The Dermooarpa prasina of Setchell (1899, p. 54) 

 is indefinite and undoubtedly most!}' what was later named I), fucicola 

 bv Saunders. 



9. Xenococcus Thur. 



Cells spherical or more or less angular due to mutual pressure 

 when closely aggregated, scattered or collected into a continuous 

 stratum, usually epiphytic ; cell contents pale blue-green or dark 

 violet, homogeneous; reproduction by cell division in two planes, and 

 by formation of gonidia. 



Thuret, Essai Class. Nost., 1875, p. 373 (nomen nudum), in Born, 

 and Thur., Notes Algol., vol. 2, 1880, pp. 73-75 (description of type) ; 

 Hansgirg, Phj'siol. u. Algol. Studien, 1887, p. Ill (lim. mut.), Prodr. 

 Algenfl. Bohm. II, 1892a., p. 128. 



The genus Xenococcus was founded by Thuret in 1880 (Notes 

 Algol., vol. 2, pp. 74, 75) upon X. Schousboei Thuret as the type 

 species, but no distinct and definite generic diagnosis was given. 

 Thuret had already mentioned the genus in 1875 (Essai Class. Nost., 

 p. 373), but neither described it nor mentioned a type species. Hans- 

 girg (1887, p. Ill) discussed Xenococcus and its limits, but set the 

 limits beyond those instituted by Thuret and repeated these later in 

 what is probably the first formal diagnosis of the genus (1892a, p. 128). 

 Bornet (in 1889 and 1892) reduced Xenococcus under Dermocarpa 

 Crouan, but Kirchner (1898, p. 58) restored it to generic rank. The 

 species of Xenococcus, as was understood by Thuret, differed from 

 those of Dermocarpa particularly in their lack of gonidangia. When 

 Batters discovered gonidangia and gonidia in Xenococcus Schousboei, 

 it seemed necessary to reduce the species under Dermocarpa, and this 

 was suggested by Bornet. Kirchner, however, brings forward the fact 

 that Xenococcus Schousboei differs from the species of Dermocarpa 

 in that the cells divide vegetatively, and consequently restores Xeno- 

 coccus to independent rank. Achille Forti (1907, p. 133) "^.tates that 

 the vegetative division is in three directions, but Thuret {in Bornet 

 and Thuret, 1880, p. 75) emphatically says that they divide perpen- 

 dicularly to the surface of the substratum and in this direction only. 

 An examination of a portion of the type material indicates cell divi- 

 sion in two directions, perpendicular to one another and to the surface 

 of the substratum. 



