24 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



branches; basal cell of determinate branches obovoid, provided with 3-4 

 branchlets, in turn with 2-3 orders of dichotomous or trichotomous 

 branchlets successively narrowed and elongated, sometimes to a hair, 

 or short and blunt; tetrasporangia subspherical, cruciate, 50-60 /x in 

 diameter, sessile on the basal cell of determinate branches; spermatia 

 arising in groups of 2-3 from the terminal cells of the determinate lateral 

 branches; four-celled carpogonial branches borne on short, fertile 

 lateral branches often reduced to a single cell; gonimoblast with 2-3 

 gonimolobes. 



Type: A collection by Bonnemaison, possibly to be found in the 

 Agardh Herbarium, Lund, Sweden. 



Type locality: "Atlantic Ocean". Probably the Atlantic coast 

 of France. 



Mexican distribution: Pacific Baja Calif. — D. 4091 (Hubbs) 

 18-30 m., D. 8230, 6-18 m., D. 8438, 8440, 47-55 m., Mason 127 (cast), 

 D. 19235 (Limbaugh & Church), 19-26 m., Isla Guadalupe; D. 10439, 

 12 mi. east of Punta Eugenio, intertidal; D. 16172 (Limbaugh), Rocas 

 Alijos, 8-28 m. (Herb. LACM). Revillagigedo Arch.—D. 4363 (A.H.F. 

 Sta. 135-34), Jan. 5, 1934, Bahia Sulphur, Isla Clarion, 47 m. 



Two forms occur among these collections, one in which the verticils 

 of lateral branches are very dense and approximate, the other in which 

 the axial cells are more elongate and the verticils distinctly separated. 

 In the former the branchlets show an ascending character and the cells 

 become quite narrow, often ending in a hair as in European material 

 illustrated by Feldmann-Mazoyer. In the latter the ascending character 

 of the branchlets is not much evident, the branchlets are more rigid, 

 shorter celled and divaricate, more like the Japanese material illustrated 

 by Okamura (1926, pi. 235). Since both forms have been found in the 

 Guadalupe Island collections it is assumed that they represent environ- 

 mental variations of this widespread tropical and subtropical species 

 known from warm waters of both the north Atlantic and north Pacific 

 and from intertidal localities down to 55 meters. 



A Working Key to the North Pacific Species of Callithamnion 

 1. Thalli with basal endophytic filaments; erect filaments to 



2 mm. high 2 



1. Plants not endophytic, mostly 2 mm. high or more 3 



2. Endophytic on fleshy algae; filaments 7-12 fx in diameter 

 C. endovagum Setch. & Gard. 



2. Endophytic on articulated corallines; filaments 20-40 /x 



in diameter C. lejolisea Farlow 



3. Plants ± prominently corticated 4 



3. Plants ecorticate, or with but a few descending filaments near 



the base 8 



