82 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



of assurgent cell rows which merge much more gradually into the erect 

 filaments of the perithallus, and the cells of the perithallus are commonly 

 in distinct periclinal layers. Furthermore, the cells of the photosynthetic 

 filaments are somewhat smaller in R. occidentalis. Examination of mate- 

 rial collected by Miss Josephine Tilden, no. 434, in Hawaii, seems to 

 show that it has structural details identical with these Mexican specimens. 

 Mexico: Is. Revilla Gigedo, common on the rocks in Braithwaite 

 Bay, I. Soccoro, no. 34-31 (plurangial, TYPE), no. 34-42 (sporangial), 

 2 Jan. 1934. Ibid., dredged from 37 meters' depth at sta. 132 near 

 Braithwaite Bay, no. 34-42A (sporangial), 2 Jan. 1934. 



Asperococcaceae 



Plants of moderate size, simple or fairly stoutly branched, flat, 

 elongate cylindrical, or of simple rounded outlines; structurally appear- 

 ing parenchymatous, the inner cells being very large and without many 

 chromatophores, the outer being much smaller, and in the assimilatory 

 layers crowded with chromatophores; sporangia and gametangia com- 

 monly developed directly from the surface cells. 



KEY TO GENERA 



1. Plant widely branched 2 



1. Plant rounded or irregularly lobed, when branched, the branches 

 close, short, generally blunt Colpomenia 



2. Plants relatively tough, the branches compressed, little tapering 

 except near the tips Chnoospora 



2. Plants of relatively delicate texture, becoming hollow, easily 

 torn, the branches tapering, terete Rosenvingea 



CHNOOSPORA J. Agardh, 1847 

 Chnoospora pacifica J. Agardh 



Taylorl942,p.51,pl.9, figs. 1,2. 



These were small plants, none being secured as large as those collected 

 in the Caribbean and recorded in 1942. 



Mexico: Nayarit, common on rocks in heavy surf on I. Maria Mag- 

 dalena, Las Tres Marias, no. 39-631, 9 May 1939. Guerrero, on rocks 

 at Ba. Petatlan, 7ios. 34-579, 34-582, 2 Mar. 1934. 



