NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 271 



This species is frequently encountered growing on beach or reef stones 

 in the northern Gulf. 



D. & R. 3373, between tide marks, Guaymas, Dec; D. 227, on shore, 

 Puerto Refugio, Jan.; D. 465, San Esteban Island, Feb.; D. 479, Puerto 

 San Carlos, near Guaymas, Feb. 



Genus LITHOTHAMNION Philippi 

 Lithothamnion australe Fosl. f. americana Foslie 



Plate 56, Figs. 5-10; Plate 57, Figs. 11-16 



Foslie, 1900, p. 13; Foslie, in Weber-van Bosse, 1904, pp. 25, 27, fig. 10. 

 Lithothamnion coralloides f. australis Foslie, 1895, p. 8, figs. 6, 7. 



Specimens of Diguet's collection from the Gulf were the basis for the 

 species Lithothamnion australe (Foslie, 1904, p. 25). They were then 

 named f. americana, as other forms were proposed from the South Pacific. 

 Some material of recent collections is undoubtedly identical with Diguet's 

 plants from the Gulf figured by Foslie (1895). The present material, 

 however, is sterile, and we can therefore only follow Foslie, who says: 

 "The question whether the forms from the East-Indian Archipelago actu- 

 ally belong to the same species as the American form is not to be settled at 

 present, the material partly in the main consisting of sterile specimens, 

 partly being too small. There are several specimens in the collection in 

 hand which are in almost full conformity with the said American form. 

 It is, however, to be observed that specimens of rather widely different 

 species may often resemble each other in habit as well as in structure, and 

 accordingly cannot be defined with certainty, when sterile. Besides it 

 cannot — as yet — be ascertained to what extent there is a connection — as 

 to this group of the algal flora — between the East-Indian Archipelago and 

 the Pacific Coast of America." 



Three collections are at hand containing specimens referable to forms 

 of this plant: D. 61, dredged in 4-6 meters, Guaymas Bay, Jan. ; D. 593a, 

 dredged in 12-26 m., San Lorenzo Channel, Feb.; D. 278a, dredged in 

 12-22 m., Mejia Channel, Puerto Refugio, Jan. 



In D. 61 the material is largely uniform and compares closely to Di- 

 guet's original specimens, also to figures of form bracchiata from the 

 South Pacific. In D. 593a there is great variation ; some material is iden- 

 tical in habit with form bracchiata, others with form ubiana and form 

 tualensis. Some with thickest branches resemble Lithothamnion monterey- 

 icum. D. 278a is a variable set similar throughout to D. 593a. 



That all this variation is produced by the same species is evident in 

 some specimens, part of which branch like form bracchiata, while an op- 

 posite side branches like form ubiana. 



