NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 103 



Mexican distribution: Pacific Baja Calif. — D. 9866, South 

 Bay, Isla Cedros, Apr. Sinaloa — D. 3674, Mazatlan, Dec. 



The material from Isla Cedros agrees particularly closely with 

 Kylin's species previously known only from Washington and from 

 Monterey, California, as well as with specimens from La Jolla and 

 from Point Fermin, Calif. Its distinctive features are its small vegeta- 

 tive cells, its somewhat sunken tetrasporangial nemathecia which are 

 more or less flush with the surface of the vegetative thallus, and the 

 relatively small, ovate tetrasporangia. 



A Cruoriella-like character of the hypothallus may develop in this 

 species due to the irregular growth of the margins over a rough sub- 

 strate such as sandstone. 



Peyssonelia guadalupensis sp. nov. 



Plate 11, figs. 5-6; Plate 33, figs. 3-4 



Thallo stricte adhaerenti, 6-10 cm. lato, exigue calcificato, rhizoidi- 

 bus multicellularibus, crassitudine valde irregulari, plerumque autem 

 300-400 IX crasso; nematheciis tetrasporangialibus elevatis, 150-200 fi 

 crassis; paraphysibus densis, tenuibus, exigue clavatis, 12-18 cellularum, 

 superiorum doleiformium, catenatis apparentibus ; tetrasporangiis lon- 

 geovatis, 100-130 ju, longis, 35-50 /x latis. 



Thalli crustose, forming closely adherent expansions of 6-10 cm. 

 over extremely irregular masses of consolidated worm tubes and cal- 

 careous debris and assuming these irregularities in their own surfaces, 

 dark, dull, purplish-red in color, lightly calcified mainly on under surface, 

 attached by numerous short, multicellular rhizoids, of extremely irregu- 

 lar thickness due to the irregularities of the substrate (180) 300-400 

 (500) /A thick, with a rather well-defined hypothallus of radially elon- 

 gated cells 16-19 fj. wide giving rise to ascending, mostly once-branched 

 perithallus cell rows; upper perithallus cells 9-11 ju. wide; tetrasporangial 

 nemathecia superficial, more or less elevated, (120) 150-200 (250) fx 

 thick; paraphyses dense, slender, slightly clavate, mostly unbranched, of 

 (10) 12-18 cells, the upper ones barrel shaped 9-10 p. diameter and 

 appearing catenate; tetrasporangia elongate-ovate, 110-130 fx long, 35- 

 50 (60) ju. wide; sexual reproduction not observed. 



Type: Holotype is Dawson 8349, Dec. 18, 1949, in box 56275, in 

 vial 2352, and on slides 1882-1887 in HAHF. 



Type locality: Outer margin of reef at extreme south tip of 

 Isla Guadalupe, Baja California. 



