NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 231 



The species is widespread along the whole coast from Costa Rica to 

 the head of the Gulf of California and is evidently a plant developing 

 long-lived annual fronds, often from perennial bases, though rapid winter 

 growth from sporelings probably accounts for by far the greater number 

 of plants. Fruiting material is most abundant in spring and summer. 



D. 538, Agua Verde Bay, Feb. ; D. 386, Tepoca Bay, Feb. ; D. 309, 

 Gonzaga Bay, Jan.; D. 139, Tiburon Island, Jan.; D. 681, July; D. 89, 

 Turner's Island, Jan.; D. 748, July; D. 413, Pond Island, Feb.; D. 

 281d, Puerto Refugio, Jan.; D. & R, 3137, Guaymas, Dec. 2, 3391, Dec. 

 22, 3239, Dec. 6, 3324a, Dec. 21, 2930, Nov. 10; D. 66, Guaymas, Jan.; 

 H. 1, San Jose del Cabo, Aug.; Poindexter, Punta Peiiasco, March. 



Padina mexicana sp. nov. 

 Plate 52, Fig. 2 



Frondes complanatae, expansae, resupinatae, late flabellatae, 1.5-4 cm. latae 

 integrae stipite basali non insigniter distincta, basim arete et prorsum per rhizinas 

 numerosas e superficie infera orientes affixae, calce incrustatae, candido-calcareo- 

 fuscae, zonatae; laminis prope margines revolutas 2 stratosis, aetate provecta 4-6 

 stratosis; pilis tantum in superficie supera; tetrasporangiis in superficie supera, in 

 lineis interruptis aut in gregariis sparsis zonas interpilas occupantibus. 



Thallus flat, expanded, resupinate, broadly flabellate, 1.5-4 cm. broad, 

 entire, without a recognizable basal stipe, attached at base and throughout 

 by numerous rhizoids from the under surface, these holding the plants 

 firmly to dense tufts of articulated corallines (Jania, Amphiroa) rather 

 heavily calcified, of a light chalky, gray-brown color, zonate, but noncalci- 

 fied piliferous lines parallel with the margins ; lamina of 2 cell layers near 

 the revolute margins, of 4-6 layers in older parts, the cells of the outer 

 layers in cross section about half as long as the inner, though this is not so 

 definite in the lower layer; hairs on upper side only; tetrasporangia borne 

 on upper surface in broken lines or scattered in groups in interpilar zones, 

 covered with a thin indusium; antheridia and oogonia unknown. 



Type : D. 725, middle and lower littoral, Turner's Island reef, off 

 Tiburon Island, July 18, 1940. Herb. AHF no. 12. 



This species is near to Padina Vickersii in color and structure, but dif- 

 fers from that and other related species in its remarkable habit of growing 

 firmly attached by its whole under surface to the irregular coralline sub- 

 strate. Overlapping laminae become firmly adherent to each other by the 

 same rhizoidal development. It is in striking contrast with P. Durvillaei 

 in all its specific characters. 



Padina mexicana is a rather short-lived summer annual, appearing 

 only with the warm-water season. It was found fairly abundant in July 



