144 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



planitie; segmentis superiorlbus 1.5-2.5 mm. latis, ter usque etiam sex- 

 iens longioribus quam latioribus, simplicibus vel rare furcatis, tenuibus 

 ad margines, sine costa; geniculis conspicuis, plerumque una cum fur- 

 cationibus sitis, ope projecturarum intergenicularum calcificatarum 

 utrimque contentis. 



ThalH saxicolous, loosely and coarsely tufted, to 5 cm. high, very 

 easily fragmented when dry, consisting of several closely spaced, 

 branched erect parts from a rather thick basal, crustose stratum; erect 

 parts cylindrical at the very base, becoming compressed and flattened 

 above, the lowermost cylindrical segments short, about 1.5 mm. in dia- 

 meter, 1.5-2.5 times as long, bearing several branches; flattened seg- 

 ments above the 2 or 3 lowermost 1.5-2.5 mm. broad, 3 to 6 times as 

 long, simple or rarely forked, thin at the edges, thicker in the middle 

 but without a midrib, without conspicuous zonal banding; branching 

 above sparsely dichotomous or trichotomous in one plane ; genicula con- 

 spicuous, usually coincident with the forkings, surrounded on two sides 

 by calcified intergenicular tissues as if by short pincers, these calcified 

 projections often growing slightly to form short knobs at the nodes, struc- 

 turally showing many (often 10 or more) tiers of cells of medullary 

 type with little or no cortical tissue; intergenicular medulla tending to 

 have an alternation of one tier of long cells with 1 tier of short cells, but 

 the short cells often elongating to nearly the length of the long cells and 

 then cutting oE a new tier of short cells; cortex thick, of 8 or more 

 anticlinal rows of small cells ; tetrasporangial conceptacles scattered over 

 flattened surfaces of segments, usually more abundant on one side than 

 the other, embedded, but causing slight, regular elevations on the sur- 

 face, the cavity about 250 /* in diameter, compressed; tetrasporangia 

 borne among congested, coarse, paraphyses ; sexual plants not seen. 



Type: Holotype is Dawson 6688, Mar. 8, 1949, in box 55390 and 

 on slides 1505 and 1506 in HAHF. 



Type locality: Rocky shore at Punta Entrada, Isla Magdalena, 

 Baja California, Mexico. 



Additional material: Baja Calif. — The type specimens repre- 

 sent the largest of three collections referable to this species. A small 

 plant with segments only 0.8-1.0 mm. broad, but with the proportions, 

 habit, branching and internal structure of the type is at hand from Isla 

 Guadalupe (D. 8334, Dec). A form of intermediate size with seg- 

 ments 1.2-1.5 mm. broad and 7-8 mm. long appears in two collections: 

 D. 6831, Cabeza Ballena, Mar., and D. 3224, Punta Palmilla, Nov. 



