NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 45 



distinct in liquid preserved material ; thallus in transection showing a 

 loosely filamentous medullary region and a firm cortex consisting of 

 large, colorless, thin-walled epidermal utricles 17-25 (30) fi broad and 

 usually somewhat taller than broad, forming a continuous surface layer 

 over the irregular hypodermal layer of small, ovate, pigmented cells 

 connected with the medullary strands; reproduction by sexual organs 

 on dioecious plants and by monospores ; cystocarps scattered throughout 

 the thallus, embedded in the outer medulla, about 200 fi in diameter, 

 with a periderm of about 4 cell layers ; antheridia in continuous, densely 

 packed superficial sori forming a dull, brownish cap over the rounded 

 tips of the ultimate branches, the antheridial pile replacing the colorless 

 layer of epidermal utricles in the sorus ; monospores borne on cystocarpic 

 plants, produced in groups of 3-4 on a small cell reaching the surface 

 from the hypodermal layer by passing between the utricle walls. 



Type: Mrs. H. D. Johnston, June 28, 1900, on sheet 96356 in the 

 Herbarium of the University of California, Berkeley. An isotype frag- 

 ment is on sheet 8895 in HAHF. 



Type locality: San Pedro, California. 



Mexican distribution: Pacific Baja Calif. — C. Johnson, Islas 

 Los Coronados, July; Williams, Apr., 1946, Laguna Ojo de Liebre 

 (Scammon), May (cystocarps and monospores); Hubbs, Johnson & 

 Allanson, Laguna de San Ignacio, Feb. (cystocarps and monospores) ; D. 

 9491, Punta Abreojos, Apr. (cystocarps) ; D. 9319, Isla Magdalena, 

 May. Gulf of Calif.— D. 661, Puerto Libertad, Feb.; D. 137-40, Isla 

 Tiburon, Jan.; D. 1673 (May), 7229 (Mar.), vicinity of Guaymas, 

 (sexual plants) ; D. 7181, Puerto Escondido, Mar. (antheridia) ; D. 

 6970 Isla Carmen, Mar. (antheridia) ; D. 6910, San Lorenzo Channel, 

 Mar.; D. 6885, Punta Frailes, Mar. (cystocarps). Nayarit — Taylor 

 39-647, Isla Maria Magdalena, May. 



This species commonly occupies the same upper sublittoral habitat as 

 Scinaia latifrons, and in the Gulf of California the two are almost al- 

 ways taken together. S. johnstoniaCj however, seems to have a wider dis- 

 tribution on the Pacific side of Baja California where S. latifrons is rare- 

 ly found. 



There seems little doubt that the antheridia reported by Setchell in 

 S. johnstoniae actually represent monosporangia. Such monosporangia 

 have been found in cystocarpic plants in the recent Mexican collections, 

 whereas the antheridia as described above, found on separate individuals, 

 are entirely unlike those of Setchell's concept. Setchell's illustration of 

 "antheridia" shows on the right hand side a good representation of a 



