142 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



at least in part, and 3-7 mm, long, rather thick in the middle and thin at 

 the irregular, somewhat undulate or lobed margins, but without a dis- 

 tinct midrib; calcification heavy; genicula prominent, less than half as 

 broad as the broader segments, consisting of 5-6 tiers (to 11 at the 

 edges) of medullary cells and an outer tissue of cortical cells; broader 

 segments tending to be dorsiventral and to have the concave surface 

 directed toward the substrate; intergenicula showing a multizonal me- 

 dulla of 2-3 (4) tiers of long cells alternating with one tier of short 

 cells, the cortex thick, of many layers of very small cells, capable of 

 thickening by secondary growth ; tetrasporangial conceptacles abundant, 

 comparatively small, the cavity about 200 /x in diameter, superficial, 

 resembling small, congested blisters, or older ones partially or wholly 

 embedded, tending to be confined to the concave under surface of the 

 broader segments, the fertile cortex capable of producing conceptacles in 

 successive annual tiers ; sexual plants not seen. 



Type : Holotype is a specimen of the St. George Expedition of 

 1923-24 in the herbarium of the Museum National d'Histoire Naturelle, 

 Paris. An isotype fragment is on sheet 54099 in HAHF. 



Type locality: Post Office Bay, Charles Island, Galapagos 

 Archipelago. 



Mexican distribution: Gulf of Calif. D. 7088, Punta Frailes, 

 Mar. ; Drouet & Richards 3387, 3389, Guaymas, Dec. Sinaloa — D. 

 3665, Mazatlan, Dec. (depauperate). Nay ark — D. 3703, Mira Mar., 

 Dec; Taylor 34-588C, Isla Isabel, Mar. Guerrero— D. 3863, 3854, 

 Acapulco, Feb. (depauperate). RevUlagigedo Archip. — Taylor 30, Isla 

 Socorro, Jan. (fragments only) ; Howell 312, (Herb. Cal. Acad. Sci.) 

 Isla Clarion, Mar. 



The irregular, broad, dorsiventral upper segments lacking a midrib 

 are distinctive in this species. 



Amphiroa brevianceps sp. nov. 

 Plate 31, fig. 2 



Thallis fasces rotundatos 2.0-3.5 cm. altos edentibus ; ramificatione 

 regularius denseque dichotoma, plus minusve in una planitie ; segmentis 

 superioribus 1.5-2 mm. latis, 2.5-4 mm. longis, marginibus tenuioribus 

 quam parte media, at sine costa ; geniculis valde prominentibus, fuscis, 

 plerumque una cum furcationibus sitis, minus dimidio latis quam parti- 

 bus contiguis calcificatis segmentorum supra infraque, quorum in medio 

 quasi fenestram late ellipticam, baud calcificatam efficientibus. 



