20 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



Type: A collection by Ellis, probably to be found in the Dillwyn 

 Herbarium in the Linnaean Society Herbarium, in Herb. Kew, or 

 Herb. Dept. of Botany, Oxford. 



Type locality: Brighton, England. 



Mexican distribution: Pacific Baja Calif. — D. 8267, Isla Guada- 

 lupe, 55-84 m. 



This material in which dwarf laterals do occur, but irregularly and 

 infrequently, provides an instance in which the merging of Antithamnion 

 and Platythamnion may be observed. See remarks under Platythamnion 

 and P. pectinatum, which is probably closely related if not conspecific 

 with this collection. 



Antithamnion pseudocorticatum sp. nov. 

 PL 7, fig. 1-5 



Thallus minutus 1-5 mm. altus, ex axibus indeterminatis prostratis 100-120 

 H diam., e cellulis 270-300 p. long, compositis, constans. Thallus ramos 

 indeterminatos erectos, per rhizoidea multicellularia longa attenuata 10-12 /t 

 diam. c. 100 fi long, unum ad aliquot e nodo affixos, efficiens; rami indeter- 

 minati erecti e cellulis 20-30 /t diam., 2-3 plo longioribus quam latae compositi, 

 distichi, ramificationem indeterminatam secondariam alternatam, intervallis 

 3-10 celularum, praebentes, omni cellula ex extremitate distali par oppositum 

 ramorum ferente; rami determinati laterales e 6-12 cellulis constantes, cellulis 

 5-10 n diam., infimis sphericis, aliis ca. 1.5-2 plo longioribus quam latae, 

 paululum incurvatis, ex omni cellula nisi ultimis 1-3 regulariter pinnati, his 

 pinnis partim ramulos breves habentibus, cacuminibus ramulorum admodum 

 obtusis; cellula basalis rami lateralis determinati par adaxiale ramulorum, 

 brevium compositorum atque ramulum unicum abaxiale primum ferens his 

 ramulis aliquamdiu meristematicis, progredienter ramosis, incurvatis, plus 

 minusve appressis, factis, involucrum laxum nodale formantibus, parte distali 

 rami lateralis determinati originalis postremo decidua; glandicellulae nullae; 

 reproductio ignota. 



Thallus minute, 1-5 mm high, consisting of prostrate indeterminate 

 axes 100-120 fi in diameter of cells 270-300 /x long, producing erect, 

 indeterminate branches attached by long, attenuated multicellular 

 rhizoids 10-12 fx in diameter, 1-several from a node, ca. 100 fx in 

 length; erect indeterminate branches of cells 20-30 /x in diameter, 2-3 

 diameters long, distichous, with alternate secondary indeterminate 

 branching at intervals of 3-10 cells, all cells bearing an opposite pair of 

 branches from their distal end; determinate lateral branches consisting 

 of 6-12 cells 5-10 jx in diameter, the lowermost spherical, the others about 

 1.5-2 diameters long, slightly incurved, regularly pinnate from each 

 cell except the last 1-3, these pinnae in part with short branchlets, the 

 branchlet tips essentially blunt; basal cell of a determinate lateral at 

 first bearing an adaxial pair of short, compound branchlets and a single 

 abaxial one, these remaining meristematic for some time, branching 

 progressively and becoming incurved, more or less appressed, and 

 forming a loose nodal envelopment, the distal part of the original 



