NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 229 



great abundance of this species was the most conspicuous feature of the 

 vegetation. Together with Padina Durvillaei and Ishige foliacea, Dicty- 

 ota Johnstonii made up the bulk of the vegetation, far surpassing the 

 young Sargassum plants in quantity. On the reef at Turner's Island the 

 change in the vegetation from that of January was even more pronounced. 

 Sargassum, which had been so conspicuous and abundant, was gone, as 

 were Colpomenia and Gigartina. Quantities of Dictyota Johnstonii clung 

 to almost every rock, and the alga was the dominant member of the sum- 

 mer flora. Many plants were over 15 cm. high, and everywhere the 

 growth was very dense. 



Though we have such a record from only a single localit}'^, it seems 

 safe to say that D. Johnstonii is a very abundant, sometimes dominant, 

 summer annual, reaching its highest development at the peak of the 

 warm-water summer season. The water temperature on the reef at Tur- 

 ner's Island was 31° C. by July 18, an increase of 15.5 degrees over the 

 temperature in January. Johnston's specimens are also large, vigorous 

 plants and probably are indicative of this species' abundance in other lo- 

 calities in the upper Gulf. 



Dictyota Vivesii Howe 



Howe, 1911,p. 497, pl.27. 



One collection from the waters of the Cape region compares favor- 

 ably with Howe's illustration of Vives' plant from La Paz. The divari- 

 cate habit, smaller size, and shorter segments distinguish this species from 

 Dictyota Johnstonii. Furthermore, the latter plant is thus far known only 

 from the coasts of the northern third of the Gulf of California. 



Though Howe does not mention anything in regard to the habitat di 

 Vives' plants, we may assume, perhaps, that they were cast up as were 

 most of his collections. Further collecting will verify whether it is con- 

 fined to the tropical waters of our coast. 



D. 623, dredged in 34-50 meters off Gorda Point, south of La Paz, 

 Feb. 



Genus NEUROGARPUS Weber & Mohr 

 Neurocarpus zonarioides (Farlow) Howe 



Farlow, 1899, p. 73; Howe, 1914, pp. 69-70; Setch. & Gard., 1924, p. 

 728; 1925, pi. 95. 

 This species was first collected in the Gulf by Johnston on high sub- 

 littoral (lower littoral) rocks at Tortuga Island. These specimens, col- 



