NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 79 



mediates that satisfactorily indicate that these are variants of a single 

 natural species. 



Pacific Baja Calif.— D. 21651, 21738, 8727, Bahia San Quintin, 

 epiphytic in shallow water. These are luxuriant, bushy plants even 

 more densely branched than the type and with somewhat shorter 

 branches. The quiet, isolated bay habitat would seem in this instance 

 to reproduce the ecological conditions under which this species thrives 

 in the Gulf of California. 



Hypoglossum retusum Dawson 

 PL 35, fig. 1-2 

 Dawson 1944, p. 107, fig. 17-18; Dawson, Neushul & Wildman 1960a, 

 p. 25. 



Thalli to 27 mm. high (or more) with a cylindrical main stripe 

 from which several blades arise irregularly as lateral branches; blades 

 oblanceolate, 11-16 mm. long, 3.5-4.5 mm. wide, attached to the main 

 stipe by a slender petiole 2-4 mm. long, monostromatic except at the 

 percurrent midrib, without lateral veins, frequently with a series of 

 rhizoids growing from the margin, with an apical notch from which the 

 apical growing point is turned backward and downward, the meristem 

 itself acute and growing by means of an apical cell; intercalary 

 divisions of primary cell row absent; initials of tertiary cell rows 

 reaching the thallus margin; reproduction not seen. 



Type: A collection of May 1944, without designated collector 

 [actually Kenneth 0. Emery] in Herb. University of California, Berkeley. 



Type locality: Rocky bottom of Kellet Channel, off south shore 

 of Isla Cedros, Baja California, Mexico, at a depth of 40-50 m. 



Mexican distribution: Pacific Baja Calif. — D. 20527 (Neushul), 

 northeast of Punta Eugenio, 35 m. 



Membranoptera spatulata Dawson 

 PL 35, fig. 5 

 Dawson 1950a, p. 157, fig. 15. 



Thalli to 1 cm. high, consisting of a dense group of small, membra- 

 nous, spatulate blades arising on short pedicels from a creeping, basal 

 portion spreading over and around branches of hydroids; blades mono- 

 stromatic except at the midrib, 2.0-2.5 mm. wide, undulate, with entire 

 margins, with abundant, pinnate, parallel, primary microscopic veins 

 and connecting secondary veins; growth by means of an apical cell; 

 intercalary division absent from primary cell row; apices rounded, the 

 apical cell forming a small apiculum; blades unbranched, or at times 

 in age more or less lacerated and lobed or branched from margins 

 near the apex; spermatangia borne in elongated sori occupying the 

 interstices between the microscopic veins over whole of the monostroma- 

 tic blade; midrib becoming heavily corticated by growth and septation 

 of very slender rhizoidal cells from the elongated cells of the primary 



