NO. I DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 57 



D. 18811, Isla Monserrate; D. 561b-40, Bahia Agua Verde; D. 565b-40, 

 Isla Espiritu Santo; Johnston 618b, San Jose del Cabo, 40 m.; D. 

 10936, Bahia Topolobampo; D. 6826, Cabeza Ballena, near San Lucas; 

 D. 3596, Mazatlan. Guerrero— D. 3842a (Hubbs), Acapulco. 



This species is closely related to the group of plants, including 

 Ceramium recticorticum. C. gracillimum var. byssoideum and C. taylorii, 

 in which the tetrasporangia are whorled and involucrate and in which 

 the cortical band is divided at about the lower third into two dis- 

 tinct parts. In C. fimbriatum the cells of this lower cortical part are 

 often horizontally elongated. 



Ceramium gracillimum var. byssoideum (Harv.) G. Mazoyer 

 PI. 20, fig. 2-3; PL 21, fig. 2-3 



G. Mazoyer 1938, p. 323; Dawson 1956, p. 53; Dawson 1959, p. 30 

 Ceramium byssoideum Harvey 1853, p. 218. Ceramium masonii Dawson 1950, 

 p. 126, pi. 2, fig. 11-12. Ceramium transversale Collins & Harvey 1917, p. 145, 

 pi. 5, fig. 29-31; Setchell & Gardner 1930, p. 170, pi. 7, fig. 23, 24. Ceramium 

 gracillimum as interpreted by Dawson 1944, p. 319. 



Thalli epiphytic, attached by rhizoids from the nodes of semi- 

 prostrate or entangled lower filaments, to 4-5 (or 10) mm. high, 40-50 

 [j. in diam., above, 60-80 /x in diam. below, corticated only at the nodes, 

 without secondary cortical expansion; branching apparently alter- 

 nate, the apices non-forcipate, slightly incurved; internodes long below, 

 to 5 times the nodal diameter; cortical bands divided in their lower 

 third by a clear line, consisting in the upper two thirds of larger, angular 

 cells cutting off a few smaller, superficial cells, the lower third of 1-2 

 tiers of horizontally elongated cells, sometimes provided with ± 

 abundant gland cells; tetrasporangia solitary to whorled, borne within 

 the cortical band which is modified by their growth to form an 

 involucre; spermatangia in whorled tufts at the nodes. 



Type: A collection by W. H. Harvey epiphytic on "gorgoniae," 

 probably in the Harvey Herbarium, Dublin, Ireland. 



Type locality: Key West, Florida 



Mexican distribution: Pacific Baja Calif.— D. 8511, 8525, 

 Hubbs 46-144, Mason 83, Isla Guadalupe; Williams 5/14/46, Isla 

 Cedros; D. 6631, Isla Margarita. Gulf of Calif.— D. 11019, Bahia San 

 Carlos; D. 470, Bahia Bocochibampo; D. 3518, Ensenada de San 

 Francisco; D. 6730, Punta Frailes; D. 3166, near Cabo Pulmo; D. 

 3442, 3417, La Paz; D. 6756, 6770, Cabeza Ballena. Guerrero— D. 

 3879, Acapulco. 



Ceramium hamatispinum Daws. 



PL 22, fig. 2-4 

 Dawson 1950, p. 122, pi. 3, fig. 20-22. 



Thalli forming entangled masses amid small, mat-dwelling algae, 

 the filaments 90-130 /x in diam., or 50-70 p in young parts, irregularly 



